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	$81.29	12.440%	$91.4025	$91.40	$91.40	$91.40
Purchase #2	$155.89	12.626%	$175.5727	$175.57	$175.55	$175.60
Purchase #3	$110.83	6.170%	$117.6682	$117.67	$117.65	$117.70
Purchase #4	$190.85	6.671%	$203.5816	$203.58	$203.60	$203.60
Purchase #5	$154.68	7.665%	$166.5362	$166.54	$166.55	$166.50
Purchase #6	$59.84	3.317%	$61.8249	$61.82	$61.80	$61.80
Purchase #7	$87.63	13.500%	$99.4601	$99.46	$99.45	$99.50
7 purchase totals =	$841.01		$916.0462	$916.04	$916.00	$916.10