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	$111.28	12.226%	$124.8851	$124.89	$124.90	$124.90
Purchase #2	$55.39	4.723%	$58.0061	$58.01	$58.00	$58.00
Purchase #3	$236.37	3.451%	$244.5271	$244.53	$244.55	$244.50
Purchase #4	$35.66	4.602%	$37.3011	$37.30	$37.30	$37.30
Purchase #5	$29.95	5.145%	$31.4909	$31.49	$31.50	$31.50
Purchase #6	$132.86	8.648%	$144.3497	$144.35	$144.35	$144.30
Purchase #7	$10.51	6.168%	$11.1583	$11.16	$11.15	$11.20
7 purchase totals =	$612.02		$651.7183	$651.73	$651.75	$651.70