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	$40.37	10.750%	$44.7098	$44.71	$44.70	$44.70
Purchase #2	$152.38	9.687%	$167.1411	$167.14	$167.15	$167.10
Purchase #3	$93.38	6.550%	$99.4964	$99.50	$99.50	$99.50
Purchase #4	$52.85	4.684%	$55.3255	$55.33	$55.35	$55.30
Purchase #5	$30.65	10.805%	$33.9617	$33.96	$33.95	$34.00
Purchase #6	$11.37	11.218%	$12.6455	$12.65	$12.65	$12.60
Purchase #7	$198.60	4.733%	$207.9997	$208.00	$208.00	$208.00
7 purchase totals =	$579.60		$621.2797	$621.29	$621.30	$621.20