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	$25.31	13.610%	$28.7547	$28.75	$28.75	$28.80
Purchase #2	$28.72	12.826%	$32.4036	$32.40	$32.40	$32.40
Purchase #3	$203.72	12.297%	$228.7714	$228.77	$228.75	$228.80
Purchase #4	$102.43	8.436%	$111.071	$111.07	$111.05	$111.10
Purchase #5	$238.73	5.870%	$252.7435	$252.74	$252.75	$252.70
Purchase #6	$217.86	12.377%	$244.8245	$244.82	$244.80	$244.80
Purchase #7	$140.50	3.576%	$145.5243	$145.52	$145.50	$145.50
7 purchase totals =	$957.27		$1,044.0930	$1,044.07	$1,044.00	$1,044.10