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	$234.79	10.642%	$259.7764	$259.78	$259.80	$259.80
Purchase #2	$33.42	12.116%	$37.4692	$37.47	$37.45	$37.50
Purchase #3	$26.70	13.343%	$30.2626	$30.26	$30.25	$30.30
Purchase #4	$139.51	5.133%	$146.671	$146.67	$146.65	$146.70
Purchase #5	$129.92	5.676%	$137.2943	$137.29	$137.30	$137.30
Purchase #6	$151.72	11.319%	$168.8932	$168.89	$168.90	$168.90
Purchase #7	$112.85	12.791%	$127.2846	$127.28	$127.30	$127.30
7 purchase totals =	$828.91		$907.6513	$907.64	$907.65	$907.80