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	$11.99	5.247%	$12.6191	$12.62	$12.60	$12.60
Purchase #2	$73.62	6.381%	$78.3177	$78.32	$78.30	$78.30
Purchase #3	$119.89	11.370%	$133.5215	$133.52	$133.50	$133.50
Purchase #4	$28.43	12.629%	$32.0204	$32.02	$32.00	$32.00
Purchase #5	$106.43	13.163%	$120.4394	$120.44	$120.45	$120.40
Purchase #6	$30.48	11.290%	$33.9212	$33.92	$33.90	$33.90
Purchase #7	$166.77	10.504%	$184.2875	$184.29	$184.30	$184.30
7 purchase totals =	$537.61		$595.1268	$595.13	$595.05	$595.00