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	$52.73	12.485%	$59.3133	$59.31	$59.30	$59.30
Purchase #2	$27.61	7.625%	$29.7153	$29.72	$29.70	$29.70
Purchase #3	$161.32	6.358%	$171.5767	$171.58	$171.60	$171.60
Purchase #4	$33.79	10.855%	$37.4579	$37.46	$37.45	$37.50
Purchase #5	$151.87	9.528%	$166.3402	$166.34	$166.35	$166.30
Purchase #6	$9.72	12.191%	$10.905	$10.91	$10.90	$10.90
Purchase #7	$161.84	8.504%	$175.6029	$175.60	$175.60	$175.60
7 purchase totals =	$598.88		$650.9113	$650.92	$650.90	$650.90