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	$139.64	13.460%	$158.4355	$158.44	$158.45	$158.40
Purchase #2	$151.37	12.472%	$170.2489	$170.25	$170.25	$170.20
Purchase #3	$26.57	8.533%	$28.8372	$28.84	$28.85	$28.80
Purchase #4	$150.50	11.530%	$167.8527	$167.85	$167.85	$167.90
Purchase #5	$158.67	9.103%	$173.1137	$173.11	$173.10	$173.10
Purchase #6	$87.99	13.455%	$99.8291	$99.83	$99.85	$99.80
Purchase #7	$215.86	13.180%	$244.3103	$244.31	$244.30	$244.30
7 purchase totals =	$930.60		$1,042.6274	$1,042.63	$1,042.65	$1,042.50