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	$234.34	12.259%	$263.0677	$263.07	$263.05	$263.10
Purchase #2	$144.36	11.183%	$160.5038	$160.50	$160.50	$160.50
Purchase #3	$148.65	7.785%	$160.2224	$160.22	$160.20	$160.20
Purchase #4	$210.37	8.164%	$227.5446	$227.54	$227.55	$227.50
Purchase #5	$40.95	10.868%	$45.4004	$45.40	$45.40	$45.40
Purchase #6	$60.52	10.530%	$66.8928	$66.89	$66.90	$66.90
Purchase #7	$11.52	7.124%	$12.3407	$12.34	$12.35	$12.30
7 purchase totals =	$850.71		$935.9724	$935.96	$935.95	$935.90