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	$244.44	3.573%	$253.1738	$253.17	$253.15	$253.20
Purchase #2	$181.43	12.217%	$203.5953	$203.60	$203.60	$203.60
Purchase #3	$127.82	13.386%	$144.93	$144.93	$144.95	$144.90
Purchase #4	$104.91	6.602%	$111.8362	$111.84	$111.85	$111.80
Purchase #5	$140.35	3.606%	$145.411	$145.41	$145.40	$145.40
Purchase #6	$6.77	7.652%	$7.288	$7.29	$7.30	$7.30
Purchase #7	$82.34	3.306%	$85.0622	$85.06	$85.05	$85.10
7 purchase totals =	$888.06		$951.2965	$951.30	$951.30	$951.30