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	$27.37	3.198%	$28.2453	$28.25	$28.25	$28.20
Purchase #2	$57.68	5.598%	$60.9089	$60.91	$60.90	$60.90
Purchase #3	$132.91	11.700%	$148.4605	$148.46	$148.45	$148.50
Purchase #4	$29.59	13.509%	$33.5873	$33.59	$33.60	$33.60
Purchase #5	$192.43	13.625%	$218.6486	$218.65	$218.65	$218.60
Purchase #6	$199.54	5.378%	$210.2713	$210.27	$210.25	$210.30
Purchase #7	$38.29	4.797%	$40.1268	$40.13	$40.15	$40.10
7 purchase totals =	$677.81		$740.2487	$740.26	$740.25	$740.20