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	$28.57	12.145%	$32.0398	$32.04	$32.05	$32.00
Purchase #2	$45.50	8.441%	$49.3407	$49.34	$49.35	$49.30
Purchase #3	$87.91	4.318%	$91.706	$91.71	$91.70	$91.70
Purchase #4	$36.70	11.331%	$40.8585	$40.86	$40.85	$40.90
Purchase #5	$130.84	12.861%	$147.6673	$147.67	$147.65	$147.70
Purchase #6	$228.34	13.389%	$258.9124	$258.91	$258.90	$258.90
Purchase #7	$56.73	5.140%	$59.6459	$59.65	$59.65	$59.60
7 purchase totals =	$614.59		$680.1706	$680.18	$680.15	$680.10