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	$242.79	3.161%	$250.4646	$250.46	$250.45	$250.50
Purchase #2	$87.92	13.362%	$99.6679	$99.67	$99.65	$99.70
Purchase #3	$130.94	6.520%	$139.4773	$139.48	$139.50	$139.50
Purchase #4	$15.60	8.698%	$16.9569	$16.96	$16.95	$17.00
Purchase #5	$151.66	12.738%	$170.9785	$170.98	$171.00	$171.00
Purchase #6	$44.50	4.433%	$46.4727	$46.47	$46.45	$46.50
Purchase #7	$34.62	8.118%	$37.4305	$37.43	$37.45	$37.40
7 purchase totals =	$708.03		$761.4484	$761.45	$761.45	$761.60