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	$51.40	8.191%	$55.6102	$55.61	$55.60	$55.60
Purchase #2	$216.29	11.713%	$241.624	$241.62	$241.60	$241.60
Purchase #3	$76.82	8.838%	$83.6094	$83.61	$83.60	$83.60
Purchase #4	$89.49	11.620%	$99.8887	$99.89	$99.90	$99.90
Purchase #5	$49.29	10.531%	$54.4807	$54.48	$54.50	$54.50
Purchase #6	$132.89	6.684%	$141.7724	$141.77	$141.75	$141.80
Purchase #7	$103.57	5.733%	$109.5077	$109.51	$109.50	$109.50
7 purchase totals =	$719.75		$786.4931	$786.49	$786.45	$786.50