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	$23.31	3.480%	$24.1212	$24.12	$24.10	$24.10
Purchase #2	$171.27	11.246%	$190.531	$190.53	$190.55	$190.50
Purchase #3	$29.92	10.471%	$33.0529	$33.05	$33.05	$33.10
Purchase #4	$111.44	11.287%	$124.0182	$124.02	$124.00	$124.00
Purchase #5	$159.95	3.438%	$165.4491	$165.45	$165.45	$165.40
Purchase #6	$40.28	6.324%	$42.8273	$42.83	$42.85	$42.80
Purchase #7	$37.70	6.431%	$40.1245	$40.12	$40.10	$40.10
7 purchase totals =	$573.87		$620.1242	$620.12	$620.10	$620.00