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	$25.70	4.634%	$26.8909	$26.89	$26.90	$26.90
Purchase #2	$62.49	3.470%	$64.6584	$64.66	$64.65	$64.70
Purchase #3	$47.85	9.334%	$52.3163	$52.32	$52.30	$52.30
Purchase #4	$35.77	13.809%	$40.7095	$40.71	$40.70	$40.70
Purchase #5	$157.62	9.580%	$172.72	$172.72	$172.70	$172.70
Purchase #6	$164.51	11.470%	$183.3793	$183.38	$183.40	$183.40
Purchase #7	$33.26	13.472%	$37.7408	$37.74	$37.75	$37.70
7 purchase totals =	$527.20		$578.4152	$578.42	$578.40	$578.40