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	$129.63	13.257%	$146.815	$146.82	$146.80	$146.80
Purchase #2	$229.55	11.509%	$255.9689	$255.97	$255.95	$256.00
Purchase #3	$132.54	10.794%	$146.8464	$146.85	$146.85	$146.80
Purchase #4	$82.89	6.482%	$88.2629	$88.26	$88.25	$88.30
Purchase #5	$33.51	10.836%	$37.1411	$37.14	$37.15	$37.10
Purchase #6	$219.31	3.738%	$227.5078	$227.51	$227.50	$227.50
Purchase #7	$44.30	3.260%	$45.7442	$45.74	$45.75	$45.70
7 purchase totals =	$871.73		$948.2863	$948.29	$948.25	$948.20