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	$11.93	13.351%	$13.5228	$13.52	$13.50	$13.50
Purchase #2	$75.77	3.578%	$78.4811	$78.48	$78.50	$78.50
Purchase #3	$144.37	11.316%	$160.7069	$160.71	$160.70	$160.70
Purchase #4	$236.56	8.183%	$255.9177	$255.92	$255.90	$255.90
Purchase #5	$18.72	10.352%	$20.6579	$20.66	$20.65	$20.70
Purchase #6	$172.43	5.585%	$182.0602	$182.06	$182.05	$182.10
Purchase #7	$152.29	5.420%	$160.5441	$160.54	$160.55	$160.50
7 purchase totals =	$812.07		$871.8907	$871.89	$871.85	$871.90