'" don't have to disclose how much HST I collected "
Yes you do.
You must remit the correct amount of taxes (GST and HST) based on the total amount that was due (whether you charge it or not). You then deduct your ITCs and remit the difference (or claim a refund if appropriate).
When audited, the tax auditor will go invoice by invoice (I know, been there, done that) to determine the taxability of each sale and then the appropriate rate of tax.
In addition, the law clearly specifies you must indicate the proper amount of GST or HST payable by the buyer on every invoice sent to buyers, together with your GST/HST number. And you should keep a copy of every invoice. If you do not, you are inviting the tax auditor to estimate the amount for you and you will not like the estimation. You then have to go to court to prove the amount is wrong. Not worth it.
For more information about GST/HST invoicing requirements, please take a look at this http://www.cra-arc.gc.ca/tx/bsnss/tpcs/gst-tps/bspsbch/itc-cti/nvc-eng.html