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	$26.39	6.787%	$28.1811	$28.18	$28.20	$28.20
Purchase #2	$80.85	5.785%	$85.5272	$85.53	$85.55	$85.50
Purchase #3	$51.47	7.356%	$55.2561	$55.26	$55.25	$55.30
Purchase #4	$178.41	6.750%	$190.4527	$190.45	$190.45	$190.50
Purchase #5	$22.82	10.496%	$25.2152	$25.22	$25.20	$25.20
Purchase #6	$127.83	12.575%	$143.9046	$143.90	$143.90	$143.90
Purchase #7	$17.55	13.346%	$19.8922	$19.89	$19.90	$19.90
7 purchase totals =	$505.32		$548.4291	$548.43	$548.45	$548.50