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	$66.67	9.409%	$72.943	$72.94	$72.95	$72.90
Purchase #2	$117.80	10.449%	$130.1089	$130.11	$130.10	$130.10
Purchase #3	$191.43	13.254%	$216.8021	$216.80	$216.80	$216.80
Purchase #4	$196.27	9.842%	$215.5869	$215.59	$215.60	$215.60
Purchase #5	$39.78	7.635%	$42.8172	$42.82	$42.80	$42.80
Purchase #6	$26.45	6.311%	$28.1193	$28.12	$28.10	$28.10
Purchase #7	$220.50	4.810%	$231.1061	$231.11	$231.10	$231.10
7 purchase totals =	$858.90		$937.4835	$937.49	$937.45	$937.40