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	$93.97	12.376%	$105.5997	$105.60	$105.60	$105.60
Purchase #2	$41.58	10.810%	$46.0748	$46.07	$46.05	$46.10
Purchase #3	$134.38	8.738%	$146.1221	$146.12	$146.10	$146.10
Purchase #4	$94.75	6.501%	$100.9097	$100.91	$100.90	$100.90
Purchase #5	$50.95	13.620%	$57.8894	$57.89	$57.90	$57.90
Purchase #6	$157.95	7.774%	$170.229	$170.23	$170.25	$170.20
Purchase #7	$33.46	7.711%	$36.0401	$36.04	$36.05	$36.00
7 purchase totals =	$607.04		$662.8648	$662.86	$662.85	$662.80