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	$76.25	9.478%	$83.477	$83.48	$83.50	$83.50
Purchase #2	$212.78	5.806%	$225.134	$225.13	$225.15	$225.10
Purchase #3	$152.93	3.700%	$158.5884	$158.59	$158.60	$158.60
Purchase #4	$32.72	8.723%	$35.5742	$35.57	$35.55	$35.60
Purchase #5	$111.42	10.508%	$123.128	$123.13	$123.15	$123.10
Purchase #6	$26.76	6.259%	$28.4349	$28.43	$28.45	$28.40
Purchase #7	$17.53	10.139%	$19.3074	$19.31	$19.30	$19.30
7 purchase totals =	$630.39		$673.6439	$673.64	$673.70	$673.60