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	$17.95	5.340%	$18.9085	$18.91	$18.90	$18.90
Purchase #2	$118.29	10.831%	$131.102	$131.10	$131.10	$131.10
Purchase #3	$172.73	11.281%	$192.2157	$192.22	$192.20	$192.20
Purchase #4	$27.42	10.451%	$30.2857	$30.29	$30.30	$30.30
Purchase #5	$155.89	5.655%	$164.7056	$164.71	$164.70	$164.70
Purchase #6	$146.82	8.171%	$158.8167	$158.82	$158.80	$158.80
Purchase #7	$129.47	7.458%	$139.1259	$139.13	$139.15	$139.10
7 purchase totals =	$768.57		$835.1601	$835.18	$835.15	$835.10