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	$90.38	8.546%	$98.1039	$98.10	$98.10	$98.10
Purchase #2	$46.39	11.485%	$51.7179	$51.72	$51.70	$51.70
Purchase #3	$244.47	12.347%	$274.6547	$274.65	$274.65	$274.70
Purchase #4	$46.92	9.603%	$51.4257	$51.43	$51.45	$51.40
Purchase #5	$165.45	10.553%	$182.9099	$182.91	$182.90	$182.90
Purchase #6	$104.26	7.252%	$111.8209	$111.82	$111.80	$111.80
Purchase #7	$53.72	3.489%	$55.5943	$55.59	$55.60	$55.60
7 purchase totals =	$751.59		$826.2273	$826.22	$826.20	$826.20