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	$216.45	11.452%	$241.2379	$241.24	$241.25	$241.20
Purchase #2	$160.62	8.425%	$174.1522	$174.15	$174.15	$174.20
Purchase #3	$86.38	6.752%	$92.2124	$92.21	$92.20	$92.20
Purchase #4	$104.72	11.560%	$116.8256	$116.83	$116.85	$116.80
Purchase #5	$35.35	6.586%	$37.6782	$37.68	$37.70	$37.70
Purchase #6	$40.35	13.721%	$45.8864	$45.89	$45.90	$45.90
Purchase #7	$83.61	10.583%	$92.4584	$92.46	$92.45	$92.50
7 purchase totals =	$727.48		$800.4511	$800.46	$800.50	$800.50