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	$33.83	10.781%	$37.4772	$37.48	$37.50	$37.50
Purchase #2	$247.83	10.111%	$272.8881	$272.89	$272.90	$272.90
Purchase #3	$53.81	4.500%	$56.2315	$56.23	$56.25	$56.20
Purchase #4	$53.99	13.209%	$61.1215	$61.12	$61.10	$61.10
Purchase #5	$94.37	6.810%	$100.7966	$100.80	$100.80	$100.80
Purchase #6	$143.84	8.170%	$155.5917	$155.59	$155.60	$155.60
Purchase #7	$132.89	9.801%	$145.9145	$145.91	$145.90	$145.90
7 purchase totals =	$760.56		$830.0211	$830.02	$830.05	$830.00