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	$239.35	3.384%	$247.4496	$247.45	$247.45	$247.40
Purchase #2	$123.64	9.426%	$135.2943	$135.29	$135.30	$135.30
Purchase #3	$55.77	10.208%	$61.463	$61.46	$61.45	$61.50
Purchase #4	$45.77	11.246%	$50.9173	$50.92	$50.90	$50.90
Purchase #5	$81.85	8.810%	$89.061	$89.06	$89.05	$89.10
Purchase #6	$157.71	10.136%	$173.6955	$173.70	$173.70	$173.70
Purchase #7	$65.63	7.142%	$70.3173	$70.32	$70.30	$70.30
7 purchase totals =	$769.72		$828.1980	$828.20	$828.15	$828.20