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	$89.79	5.370%	$94.6117	$94.61	$94.60	$94.60
Purchase #2	$150.49	7.219%	$161.3539	$161.35	$161.35	$161.40
Purchase #3	$99.36	5.583%	$104.9073	$104.91	$104.90	$104.90
Purchase #4	$41.29	9.511%	$45.2171	$45.22	$45.20	$45.20
Purchase #5	$95.78	5.276%	$100.8334	$100.83	$100.85	$100.80
Purchase #6	$191.77	13.344%	$217.3598	$217.36	$217.35	$217.40
Purchase #7	$132.57	10.572%	$146.5853	$146.59	$146.60	$146.60
7 purchase totals =	$801.05		$870.8685	$870.87	$870.85	$870.90