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	$9.68	12.211%	$10.862	$10.86	$10.85	$10.90
Purchase #2	$48.73	5.534%	$51.4267	$51.43	$51.45	$51.40
Purchase #3	$107.93	10.851%	$119.6415	$119.64	$119.65	$119.60
Purchase #4	$88.53	12.190%	$99.3218	$99.32	$99.30	$99.30
Purchase #5	$227.87	11.593%	$254.287	$254.29	$254.30	$254.30
Purchase #6	$140.88	10.669%	$155.9105	$155.91	$155.90	$155.90
Purchase #7	$131.92	11.257%	$146.7702	$146.77	$146.75	$146.80
7 purchase totals =	$755.54		$838.2197	$838.22	$838.20	$838.20