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	$167.86	7.593%	$180.6056	$180.61	$180.60	$180.60
Purchase #2	$159.57	8.864%	$173.7143	$173.71	$173.70	$173.70
Purchase #3	$223.61	8.444%	$242.4916	$242.49	$242.50	$242.50
Purchase #4	$41.86	7.718%	$45.0908	$45.09	$45.10	$45.10
Purchase #5	$87.95	13.309%	$99.6553	$99.66	$99.65	$99.70
Purchase #6	$33.87	12.505%	$38.1054	$38.11	$38.10	$38.10
Purchase #7	$49.72	13.614%	$56.4889	$56.49	$56.50	$56.50
7 purchase totals =	$764.44		$836.1519	$836.16	$836.15	$836.20