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	$159.29	6.769%	$170.0723	$170.07	$170.05	$170.10
Purchase #2	$90.54	9.810%	$99.422	$99.42	$99.40	$99.40
Purchase #3	$206.88	5.790%	$218.8584	$218.86	$218.85	$218.90
Purchase #4	$189.58	10.468%	$209.4252	$209.43	$209.45	$209.40
Purchase #5	$176.54	8.604%	$191.7295	$191.73	$191.75	$191.70
Purchase #6	$188.37	10.422%	$208.0019	$208.00	$208.00	$208.00
Purchase #7	$160.55	7.510%	$172.6073	$172.61	$172.60	$172.60
7 purchase totals =	$1,171.75		$1,270.1166	$1,270.12	$1,270.10	$1,270.10