Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$32.56	12.233%	$36.5431	$36.54	$36.55	$36.50
Purchase #2	$127.99	9.622%	$140.3052	$140.31	$140.30	$140.30
Purchase #3	$70.79	13.725%	$80.5059	$80.51	$80.50	$80.50
Purchase #4	$50.61	3.805%	$52.5357	$52.54	$52.55	$52.50
Purchase #5	$109.49	12.863%	$123.5737	$123.57	$123.55	$123.60
Purchase #6	$134.77	12.791%	$152.0084	$152.01	$152.00	$152.00
Purchase #7	$68.49	8.859%	$74.5575	$74.56	$74.55	$74.60
7 purchase totals =	$594.70		$660.0295	$660.04	$660.00	$660.00