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	$223.70	7.505%	$240.4887	$240.49	$240.50	$240.50
Purchase #2	$195.67	13.643%	$222.3653	$222.37	$222.35	$222.40
Purchase #3	$194.34	11.125%	$215.9603	$215.96	$215.95	$216.00
Purchase #4	$132.91	4.844%	$139.3482	$139.35	$139.35	$139.30
Purchase #5	$81.51	9.352%	$89.1328	$89.13	$89.15	$89.10
Purchase #6	$244.34	13.819%	$278.1053	$278.11	$278.10	$278.10
Purchase #7	$60.50	11.865%	$67.6783	$67.68	$67.70	$67.70
7 purchase totals =	$1,132.97		$1,253.0789	$1,253.09	$1,253.10	$1,253.10