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	$102.55	5.797%	$108.4948	$108.49	$108.50	$108.50
Purchase #2	$82.31	13.592%	$93.4976	$93.50	$93.50	$93.50
Purchase #3	$132.57	10.749%	$146.8199	$146.82	$146.80	$146.80
Purchase #4	$173.60	4.560%	$181.5162	$181.52	$181.50	$181.50
Purchase #5	$144.65	10.473%	$159.7992	$159.80	$159.80	$159.80
Purchase #6	$159.66	10.333%	$176.1577	$176.16	$176.15	$176.20
Purchase #7	$59.49	9.334%	$65.0428	$65.04	$65.05	$65.00
7 purchase totals =	$854.83		$931.3282	$931.33	$931.30	$931.30