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	$36.39	4.855%	$38.1567	$38.16	$38.15	$38.20
Purchase #2	$152.74	5.449%	$161.0628	$161.06	$161.05	$161.10
Purchase #3	$140.35	7.660%	$151.1008	$151.10	$151.10	$151.10
Purchase #4	$48.29	11.282%	$53.7381	$53.74	$53.75	$53.70
Purchase #5	$123.84	12.609%	$139.455	$139.46	$139.45	$139.50
Purchase #6	$191.28	9.530%	$209.509	$209.51	$209.50	$209.50
Purchase #7	$12.72	4.188%	$13.2527	$13.25	$13.25	$13.30
7 purchase totals =	$705.61		$766.2751	$766.28	$766.25	$766.40