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	$169.51	11.648%	$189.2545	$189.25	$189.25	$189.30
Purchase #2	$131.34	11.707%	$146.716	$146.72	$146.70	$146.70
Purchase #3	$70.50	11.581%	$78.6646	$78.66	$78.65	$78.70
Purchase #4	$246.34	6.163%	$261.5219	$261.52	$261.50	$261.50
Purchase #5	$54.89	5.551%	$57.9369	$57.94	$57.95	$57.90
Purchase #6	$206.33	11.327%	$229.701	$229.70	$229.70	$229.70
Purchase #7	$10.68	8.749%	$11.6144	$11.61	$11.60	$11.60
7 purchase totals =	$889.59		$975.4093	$975.40	$975.35	$975.40