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	$131.82	9.369%	$144.1702	$144.17	$144.15	$144.20
Purchase #2	$172.33	10.490%	$190.4074	$190.41	$190.40	$190.40
Purchase #3	$202.42	12.834%	$228.3986	$228.40	$228.40	$228.40
Purchase #4	$68.33	4.433%	$71.3591	$71.36	$71.35	$71.40
Purchase #5	$169.51	8.786%	$184.4031	$184.40	$184.40	$184.40
Purchase #6	$62.75	13.594%	$71.2802	$71.28	$71.30	$71.30
Purchase #7	$74.77	9.406%	$81.8029	$81.80	$81.80	$81.80
7 purchase totals =	$881.93		$971.8215	$971.82	$971.80	$971.90