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	$137.51	6.252%	$146.1071	$146.11	$146.10	$146.10
Purchase #2	$130.36	13.139%	$147.488	$147.49	$147.50	$147.50
Purchase #3	$246.58	11.449%	$274.8109	$274.81	$274.80	$274.80
Purchase #4	$16.59	10.791%	$18.3802	$18.38	$18.40	$18.40
Purchase #5	$133.85	13.342%	$151.7083	$151.71	$151.70	$151.70
Purchase #6	$24.96	13.571%	$28.3473	$28.35	$28.35	$28.30
Purchase #7	$146.51	13.790%	$166.7137	$166.71	$166.70	$166.70
7 purchase totals =	$836.36		$933.5555	$933.56	$933.55	$933.50