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	$83.38	11.662%	$93.1038	$93.10	$93.10	$93.10
Purchase #2	$110.39	12.857%	$124.5828	$124.58	$124.60	$124.60
Purchase #3	$147.42	9.547%	$161.4942	$161.49	$161.50	$161.50
Purchase #4	$18.55	10.369%	$20.4734	$20.47	$20.45	$20.50
Purchase #5	$95.28	10.795%	$105.5655	$105.57	$105.55	$105.60
Purchase #6	$229.94	13.475%	$260.9244	$260.92	$260.90	$260.90
Purchase #7	$32.63	9.378%	$35.69	$35.69	$35.70	$35.70
7 purchase totals =	$717.59		$801.8341	$801.82	$801.80	$801.90