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	$38.91	6.183%	$41.3158	$41.32	$41.30	$41.30
Purchase #2	$85.85	5.775%	$90.8078	$90.81	$90.80	$90.80
Purchase #3	$186.58	13.162%	$211.1377	$211.14	$211.15	$211.10
Purchase #4	$237.32	11.592%	$264.8301	$264.83	$264.85	$264.80
Purchase #5	$81.67	6.185%	$86.7213	$86.72	$86.70	$86.70
Purchase #6	$32.43	11.795%	$36.2551	$36.26	$36.25	$36.30
Purchase #7	$115.59	7.668%	$124.4534	$124.45	$124.45	$124.50
7 purchase totals =	$778.35		$855.5212	$855.53	$855.50	$855.50