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	$65.96	9.758%	$72.3964	$72.40	$72.40	$72.40
Purchase #2	$105.57	4.491%	$110.3111	$110.31	$110.30	$110.30
Purchase #3	$125.81	12.801%	$141.9149	$141.91	$141.90	$141.90
Purchase #4	$121.31	9.801%	$133.1996	$133.20	$133.20	$133.20
Purchase #5	$20.37	7.261%	$21.8491	$21.85	$21.85	$21.80
Purchase #6	$67.57	13.539%	$76.7183	$76.72	$76.70	$76.70
Purchase #7	$149.73	10.312%	$165.1702	$165.17	$165.15	$165.20
7 purchase totals =	$656.32		$721.5596	$721.56	$721.50	$721.50