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	$36.34	11.625%	$40.5645	$40.56	$40.55	$40.60
Purchase #2	$78.81	12.343%	$88.5375	$88.54	$88.55	$88.50
Purchase #3	$37.67	13.211%	$42.6466	$42.65	$42.65	$42.60
Purchase #4	$212.75	4.404%	$222.1195	$222.12	$222.10	$222.10
Purchase #5	$21.50	5.680%	$22.7212	$22.72	$22.70	$22.70
Purchase #6	$177.30	4.618%	$185.4877	$185.49	$185.50	$185.50
Purchase #7	$192.25	13.521%	$218.2441	$218.24	$218.25	$218.20
7 purchase totals =	$756.62		$820.3211	$820.32	$820.30	$820.20