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	$215.43	12.727%	$242.8478	$242.85	$242.85	$242.80
Purchase #2	$10.72	13.662%	$12.1846	$12.18	$12.20	$12.20
Purchase #3	$80.72	12.462%	$90.7793	$90.78	$90.80	$90.80
Purchase #4	$139.67	4.631%	$146.1381	$146.14	$146.15	$146.10
Purchase #5	$149.45	10.769%	$165.5443	$165.54	$165.55	$165.50
Purchase #6	$76.66	5.665%	$81.0028	$81.00	$81.00	$81.00
Purchase #7	$135.37	12.117%	$151.7728	$151.77	$151.75	$151.80
7 purchase totals =	$808.02		$890.2697	$890.26	$890.30	$890.20