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	$26.40	3.744%	$27.3884	$27.39	$27.40	$27.40
Purchase #2	$234.31	3.338%	$242.1313	$242.13	$242.15	$242.10
Purchase #3	$105.57	13.594%	$119.9212	$119.92	$119.90	$119.90
Purchase #4	$205.53	8.642%	$223.2919	$223.29	$223.30	$223.30
Purchase #5	$105.65	4.596%	$110.5057	$110.51	$110.50	$110.50
Purchase #6	$11.59	3.346%	$11.9778	$11.98	$12.00	$12.00
Purchase #7	$56.86	10.635%	$62.9071	$62.91	$62.90	$62.90
7 purchase totals =	$745.91		$798.1234	$798.13	$798.15	$798.10