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	$221.37	13.197%	$250.5842	$250.58	$250.60	$250.60
Purchase #2	$18.74	12.370%	$21.0581	$21.06	$21.05	$21.10
Purchase #3	$221.76	11.351%	$246.932	$246.93	$246.95	$246.90
Purchase #4	$230.73	4.241%	$240.5153	$240.52	$240.50	$240.50
Purchase #5	$52.86	13.808%	$60.1589	$60.16	$60.15	$60.20
Purchase #6	$223.73	7.309%	$240.0824	$240.08	$240.10	$240.10
Purchase #7	$32.75	13.847%	$37.2849	$37.28	$37.30	$37.30
7 purchase totals =	$1,001.94		$1,096.6158	$1,096.61	$1,096.65	$1,096.70