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	$88.73	13.281%	$100.5142	$100.51	$100.50	$100.50
Purchase #2	$93.69	6.505%	$99.7845	$99.78	$99.80	$99.80
Purchase #3	$192.66	13.692%	$219.039	$219.04	$219.05	$219.00
Purchase #4	$213.76	13.560%	$242.7459	$242.75	$242.75	$242.70
Purchase #5	$104.53	12.140%	$117.2199	$117.22	$117.20	$117.20
Purchase #6	$127.57	9.123%	$139.2082	$139.21	$139.20	$139.20
Purchase #7	$25.52	4.104%	$26.5673	$26.57	$26.55	$26.60
7 purchase totals =	$846.46		$945.0790	$945.08	$945.05	$945.00