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	$235.51	12.483%	$264.9087	$264.91	$264.90	$264.90
Purchase #2	$87.40	3.739%	$90.6679	$90.67	$90.65	$90.70
Purchase #3	$140.31	7.146%	$150.3366	$150.34	$150.35	$150.30
Purchase #4	$169.84	13.692%	$193.0945	$193.09	$193.10	$193.10
Purchase #5	$38.85	8.683%	$42.2233	$42.22	$42.20	$42.20
Purchase #6	$188.83	5.544%	$199.2987	$199.30	$199.30	$199.30
Purchase #7	$37.72	10.125%	$41.5392	$41.54	$41.55	$41.50
7 purchase totals =	$898.46		$982.0689	$982.07	$982.05	$982.00