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	$39.91	12.512%	$44.9035	$44.90	$44.90	$44.90
Purchase #2	$200.27	10.377%	$221.052	$221.05	$221.05	$221.10
Purchase #3	$15.54	13.294%	$17.6059	$17.61	$17.60	$17.60
Purchase #4	$57.57	12.698%	$64.8802	$64.88	$64.90	$64.90
Purchase #5	$127.48	12.442%	$143.3411	$143.34	$143.35	$143.30
Purchase #6	$79.82	12.485%	$89.7855	$89.79	$89.80	$89.80
Purchase #7	$158.29	12.505%	$178.0842	$178.08	$178.10	$178.10
7 purchase totals =	$678.88		$759.6524	$759.65	$759.70	$759.70