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	$164.35	3.798%	$170.592	$170.59	$170.60	$170.60
Purchase #2	$37.30	10.568%	$41.2419	$41.24	$41.25	$41.20
Purchase #3	$50.85	3.121%	$52.437	$52.44	$52.45	$52.40
Purchase #4	$199.48	11.625%	$222.6696	$222.67	$222.65	$222.70
Purchase #5	$243.33	9.301%	$265.9621	$265.96	$265.95	$266.00
Purchase #6	$93.26	10.520%	$103.071	$103.07	$103.05	$103.10
Purchase #7	$107.53	5.522%	$113.4678	$113.47	$113.45	$113.50
7 purchase totals =	$896.10		$969.4414	$969.44	$969.40	$969.50