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	$221.90	12.431%	$249.4844	$249.48	$249.50	$249.50
Purchase #2	$151.99	11.871%	$170.0327	$170.03	$170.05	$170.00
Purchase #3	$116.52	10.385%	$128.6206	$128.62	$128.60	$128.60
Purchase #4	$137.94	11.315%	$153.5479	$153.55	$153.55	$153.50
Purchase #5	$80.58	12.227%	$90.4325	$90.43	$90.45	$90.40
Purchase #6	$40.45	12.501%	$45.5067	$45.51	$45.50	$45.50
Purchase #7	$78.67	8.827%	$85.6142	$85.61	$85.60	$85.60
7 purchase totals =	$828.05		$923.2390	$923.23	$923.25	$923.10