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	$133.82	9.485%	$146.5128	$146.51	$146.50	$146.50
Purchase #2	$108.85	9.719%	$119.4291	$119.43	$119.45	$119.40
Purchase #3	$66.77	7.447%	$71.7424	$71.74	$71.75	$71.70
Purchase #4	$130.95	5.477%	$138.1221	$138.12	$138.10	$138.10
Purchase #5	$38.44	7.752%	$41.4199	$41.42	$41.40	$41.40
Purchase #6	$81.54	4.273%	$85.0242	$85.02	$85.00	$85.00
Purchase #7	$34.80	13.432%	$39.4743	$39.47	$39.45	$39.50
7 purchase totals =	$595.17		$641.7248	$641.71	$641.65	$641.60