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	$198.79	12.293%	$223.2273	$223.23	$223.25	$223.20
Purchase #2	$33.27	11.679%	$37.1556	$37.16	$37.15	$37.20
Purchase #3	$107.84	10.755%	$119.4382	$119.44	$119.45	$119.40
Purchase #4	$82.33	12.796%	$92.8649	$92.86	$92.85	$92.90
Purchase #5	$63.83	4.103%	$66.4489	$66.45	$66.45	$66.40
Purchase #6	$59.67	10.373%	$65.8596	$65.86	$65.85	$65.90
Purchase #7	$152.42	13.238%	$172.5974	$172.60	$172.60	$172.60
7 purchase totals =	$698.15		$777.5919	$777.60	$777.60	$777.60