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	$35.92	4.267%	$37.4527	$37.45	$37.45	$37.50
Purchase #2	$74.29	8.537%	$80.6321	$80.63	$80.65	$80.60
Purchase #3	$33.72	10.500%	$37.2606	$37.26	$37.25	$37.30
Purchase #4	$159.83	13.337%	$181.1465	$181.15	$181.15	$181.10
Purchase #5	$41.42	10.865%	$45.9203	$45.92	$45.90	$45.90
Purchase #6	$143.92	3.235%	$148.5758	$148.58	$148.60	$148.60
Purchase #7	$113.78	13.381%	$129.0049	$129.00	$129.00	$129.00
7 purchase totals =	$602.88		$659.9929	$659.99	$660.00	$660.00