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	$111.96	11.239%	$124.5432	$124.54	$124.55	$124.50
Purchase #2	$217.80	13.822%	$247.9043	$247.90	$247.90	$247.90
Purchase #3	$190.59	13.601%	$216.5121	$216.51	$216.50	$216.50
Purchase #4	$237.94	11.225%	$264.6488	$264.65	$264.65	$264.60
Purchase #5	$159.90	3.140%	$164.9209	$164.92	$164.90	$164.90
Purchase #6	$169.50	4.680%	$177.4326	$177.43	$177.45	$177.40
Purchase #7	$120.83	13.571%	$137.2278	$137.23	$137.25	$137.20
7 purchase totals =	$1,208.52		$1,333.1897	$1,333.18	$1,333.20	$1,333.00