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	$238.39	7.257%	$255.69	$255.69	$255.70	$255.70
Purchase #2	$143.72	6.760%	$153.4355	$153.44	$153.45	$153.40
Purchase #3	$121.96	7.852%	$131.5363	$131.54	$131.55	$131.50
Purchase #4	$126.45	11.624%	$141.1485	$141.15	$141.15	$141.10
Purchase #5	$67.85	9.405%	$74.2313	$74.23	$74.25	$74.20
Purchase #6	$94.77	8.797%	$103.1069	$103.11	$103.10	$103.10
Purchase #7	$53.78	6.445%	$57.2461	$57.25	$57.25	$57.20
7 purchase totals =	$846.92		$916.3946	$916.41	$916.45	$916.20