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	$87.91	12.438%	$98.8442	$98.84	$98.85	$98.80
Purchase #2	$100.96	10.371%	$111.4306	$111.43	$111.45	$111.40
Purchase #3	$15.48	10.162%	$17.0531	$17.05	$17.05	$17.10
Purchase #4	$208.37	6.673%	$222.2745	$222.27	$222.25	$222.30
Purchase #5	$104.58	13.281%	$118.4693	$118.47	$118.45	$118.50
Purchase #6	$183.62	7.250%	$196.9325	$196.93	$196.95	$196.90
Purchase #7	$117.48	10.679%	$130.0257	$130.03	$130.05	$130.00
7 purchase totals =	$818.40		$895.0299	$895.02	$895.05	$895.00