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	$58.37	12.208%	$65.4958	$65.50	$65.50	$65.50
Purchase #2	$172.95	12.562%	$194.676	$194.68	$194.70	$194.70
Purchase #3	$160.86	12.176%	$180.4463	$180.45	$180.45	$180.40
Purchase #4	$57.73	4.710%	$60.4491	$60.45	$60.45	$60.40
Purchase #5	$93.25	13.143%	$105.5058	$105.51	$105.50	$105.50
Purchase #6	$27.79	13.259%	$31.4747	$31.47	$31.45	$31.50
Purchase #7	$77.40	13.782%	$88.0673	$88.07	$88.05	$88.10
7 purchase totals =	$648.35		$726.1150	$726.13	$726.10	$726.10