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	$99.40	9.766%	$109.1074	$109.11	$109.10	$109.10
Purchase #2	$71.39	13.247%	$80.847	$80.85	$80.85	$80.80
Purchase #3	$21.33	3.806%	$22.1418	$22.14	$22.15	$22.10
Purchase #4	$108.63	13.485%	$123.2788	$123.28	$123.30	$123.30
Purchase #5	$203.36	6.470%	$216.5174	$216.52	$216.50	$216.50
Purchase #6	$187.70	12.110%	$210.4305	$210.43	$210.45	$210.40
Purchase #7	$185.96	10.718%	$205.8912	$205.89	$205.90	$205.90
7 purchase totals =	$877.77		$968.2141	$968.22	$968.25	$968.10