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	$70.88	13.521%	$80.4637	$80.46	$80.45	$80.50
Purchase #2	$28.35	11.282%	$31.5484	$31.55	$31.55	$31.50
Purchase #3	$155.97	10.568%	$172.4529	$172.45	$172.45	$172.50
Purchase #4	$194.50	7.476%	$209.0408	$209.04	$209.05	$209.00
Purchase #5	$82.66	12.662%	$93.1264	$93.13	$93.15	$93.10
Purchase #6	$40.84	10.358%	$45.0702	$45.07	$45.05	$45.10
Purchase #7	$161.36	3.624%	$167.2077	$167.21	$167.20	$167.20
7 purchase totals =	$734.56		$798.9101	$798.91	$798.90	$798.90