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	$247.29	13.191%	$279.91	$279.91	$279.90	$279.90
Purchase #2	$167.29	12.769%	$188.6513	$188.65	$188.65	$188.70
Purchase #3	$87.51	8.433%	$94.8897	$94.89	$94.90	$94.90
Purchase #4	$21.67	5.419%	$22.8443	$22.84	$22.85	$22.80
Purchase #5	$89.35	7.547%	$96.0932	$96.09	$96.10	$96.10
Purchase #6	$172.40	10.725%	$190.8899	$190.89	$190.90	$190.90
Purchase #7	$196.56	4.113%	$204.6445	$204.64	$204.65	$204.60
7 purchase totals =	$982.07		$1,077.9229	$1,077.91	$1,077.95	$1,077.90