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	$12.28	4.363%	$12.8158	$12.82	$12.80	$12.80
Purchase #2	$231.32	7.446%	$248.5441	$248.54	$248.55	$248.50
Purchase #3	$32.57	13.781%	$37.0585	$37.06	$37.05	$37.10
Purchase #4	$153.32	10.265%	$169.0583	$169.06	$169.05	$169.10
Purchase #5	$15.69	6.746%	$16.7484	$16.75	$16.75	$16.70
Purchase #6	$89.50	6.647%	$95.4491	$95.45	$95.45	$95.40
Purchase #7	$158.39	9.784%	$173.8869	$173.89	$173.90	$173.90
7 purchase totals =	$693.07		$753.5611	$753.57	$753.55	$753.50