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	$72.31	13.653%	$82.1825	$82.18	$82.20	$82.20
Purchase #2	$238.43	4.598%	$249.393	$249.39	$249.40	$249.40
Purchase #3	$219.39	10.513%	$242.4545	$242.45	$242.45	$242.50
Purchase #4	$141.46	8.105%	$152.9253	$152.93	$152.95	$152.90
Purchase #5	$177.55	10.359%	$195.9424	$195.94	$195.95	$195.90
Purchase #6	$235.53	11.539%	$262.7078	$262.71	$262.70	$262.70
Purchase #7	$141.58	6.864%	$151.2981	$151.30	$151.30	$151.30
7 purchase totals =	$1,226.25		$1,336.9036	$1,336.90	$1,336.95	$1,336.90