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	$32.60	13.636%	$37.0453	$37.05	$37.05	$37.00
Purchase #2	$97.78	3.182%	$100.8914	$100.89	$100.90	$100.90
Purchase #3	$172.96	10.339%	$190.8423	$190.84	$190.85	$190.80
Purchase #4	$88.41	12.773%	$99.7026	$99.70	$99.70	$99.70
Purchase #5	$75.61	7.862%	$81.5545	$81.55	$81.55	$81.60
Purchase #6	$229.75	10.737%	$254.4183	$254.42	$254.40	$254.40
Purchase #7	$110.81	13.552%	$125.827	$125.83	$125.85	$125.80
7 purchase totals =	$807.92		$890.2814	$890.28	$890.30	$890.20