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	$125.96	13.785%	$143.3236	$143.32	$143.30	$143.30
Purchase #2	$83.45	3.223%	$86.1396	$86.14	$86.15	$86.10
Purchase #3	$141.74	8.496%	$153.7822	$153.78	$153.80	$153.80
Purchase #4	$192.79	3.143%	$198.8494	$198.85	$198.85	$198.80
Purchase #5	$216.38	11.543%	$241.3567	$241.36	$241.35	$241.40
Purchase #6	$91.78	12.780%	$103.5095	$103.51	$103.50	$103.50
Purchase #7	$228.42	5.606%	$241.2252	$241.23	$241.25	$241.20
7 purchase totals =	$1,080.52		$1,168.1862	$1,168.19	$1,168.20	$1,168.10