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	$100.43	5.143%	$105.5951	$105.60	$105.60	$105.60
Purchase #2	$67.76	8.145%	$73.2791	$73.28	$73.30	$73.30
Purchase #3	$125.93	10.806%	$139.538	$139.54	$139.55	$139.50
Purchase #4	$50.48	13.766%	$57.4291	$57.43	$57.45	$57.40
Purchase #5	$5.43	11.559%	$6.0577	$6.06	$6.05	$6.10
Purchase #6	$188.68	10.528%	$208.5442	$208.54	$208.55	$208.50
Purchase #7	$35.45	10.427%	$39.1464	$39.15	$39.15	$39.10
7 purchase totals =	$574.16		$629.5896	$629.60	$629.65	$629.50