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	$30.29	13.506%	$34.381	$34.38	$34.40	$34.40
Purchase #2	$143.57	8.617%	$155.9414	$155.94	$155.95	$155.90
Purchase #3	$193.62	7.662%	$208.4552	$208.46	$208.45	$208.50
Purchase #4	$78.52	8.625%	$85.2924	$85.29	$85.30	$85.30
Purchase #5	$45.46	13.376%	$51.5407	$51.54	$51.55	$51.50
Purchase #6	$72.67	4.680%	$76.071	$76.07	$76.05	$76.10
Purchase #7	$81.42	10.312%	$89.816	$89.82	$89.80	$89.80
7 purchase totals =	$645.55		$701.4977	$701.50	$701.50	$701.50