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	$77.59	13.593%	$88.1368	$88.14	$88.15	$88.10
Purchase #2	$114.61	8.230%	$124.0424	$124.04	$124.05	$124.00
Purchase #3	$89.88	12.556%	$101.1653	$101.17	$101.15	$101.20
Purchase #4	$30.29	7.496%	$32.5605	$32.56	$32.55	$32.60
Purchase #5	$37.89	10.672%	$41.9336	$41.93	$41.95	$41.90
Purchase #6	$10.59	10.667%	$11.7196	$11.72	$11.70	$11.70
Purchase #7	$203.30	6.159%	$215.8212	$215.82	$215.80	$215.80
7 purchase totals =	$564.15		$615.3794	$615.38	$615.35	$615.30