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	$106.32	5.189%	$111.8369	$111.84	$111.85	$111.80
Purchase #2	$55.65	6.742%	$59.4019	$59.40	$59.40	$59.40
Purchase #3	$218.58	11.328%	$243.3407	$243.34	$243.35	$243.30
Purchase #4	$139.47	8.614%	$151.4839	$151.48	$151.50	$151.50
Purchase #5	$216.87	6.102%	$230.1034	$230.10	$230.10	$230.10
Purchase #6	$127.32	13.622%	$144.6635	$144.66	$144.65	$144.70
Purchase #7	$16.91	3.324%	$17.4721	$17.47	$17.45	$17.50
7 purchase totals =	$881.12		$958.3024	$958.29	$958.30	$958.30