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	$100.30	6.246%	$106.5647	$106.56	$106.55	$106.60
Purchase #2	$224.40	6.350%	$238.6494	$238.65	$238.65	$238.60
Purchase #3	$208.86	11.727%	$233.353	$233.35	$233.35	$233.40
Purchase #4	$30.99	8.153%	$33.5166	$33.52	$33.50	$33.50
Purchase #5	$90.76	10.502%	$100.2916	$100.29	$100.30	$100.30
Purchase #6	$146.27	5.631%	$154.5065	$154.51	$154.50	$154.50
Purchase #7	$32.97	9.760%	$36.1879	$36.19	$36.20	$36.20
7 purchase totals =	$834.55		$903.0697	$903.07	$903.05	$903.10