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	$136.30	6.409%	$145.0355	$145.04	$145.05	$145.00
Purchase #2	$64.93	10.604%	$71.8152	$71.82	$71.80	$71.80
Purchase #3	$146.84	12.848%	$165.706	$165.71	$165.70	$165.70
Purchase #4	$12.78	4.180%	$13.3142	$13.31	$13.30	$13.30
Purchase #5	$149.34	10.383%	$164.846	$164.85	$164.85	$164.80
Purchase #6	$157.56	10.142%	$173.5397	$173.54	$173.55	$173.50
Purchase #7	$40.35	9.516%	$44.1897	$44.19	$44.20	$44.20
7 purchase totals =	$708.10		$778.4463	$778.46	$778.45	$778.30