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	$128.55	13.813%	$146.3066	$146.31	$146.30	$146.30
Purchase #2	$63.82	6.160%	$67.7513	$67.75	$67.75	$67.80
Purchase #3	$211.30	7.564%	$227.2827	$227.28	$227.30	$227.30
Purchase #4	$87.80	3.815%	$91.1496	$91.15	$91.15	$91.10
Purchase #5	$68.81	9.753%	$75.521	$75.52	$75.50	$75.50
Purchase #6	$90.50	5.832%	$95.778	$95.78	$95.80	$95.80
Purchase #7	$32.39	4.436%	$33.8268	$33.83	$33.85	$33.80
7 purchase totals =	$683.17		$737.6160	$737.62	$737.65	$737.60