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	$190.66	11.422%	$212.4372	$212.44	$212.45	$212.40
Purchase #2	$79.42	4.806%	$83.2369	$83.24	$83.25	$83.20
Purchase #3	$121.26	10.290%	$133.7377	$133.74	$133.75	$133.70
Purchase #4	$124.50	4.664%	$130.3067	$130.31	$130.30	$130.30
Purchase #5	$37.38	9.105%	$40.7834	$40.78	$40.80	$40.80
Purchase #6	$55.71	7.514%	$59.896	$59.90	$59.90	$59.90
Purchase #7	$158.75	9.218%	$173.3836	$173.38	$173.40	$173.40
7 purchase totals =	$767.68		$833.7815	$833.79	$833.85	$833.70