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	$32.35	12.864%	$36.5115	$36.51	$36.50	$36.50
Purchase #2	$214.93	3.770%	$223.0329	$223.03	$223.05	$223.00
Purchase #3	$199.59	8.528%	$216.611	$216.61	$216.60	$216.60
Purchase #4	$99.78	3.485%	$103.2573	$103.26	$103.25	$103.30
Purchase #5	$57.25	4.488%	$59.8194	$59.82	$59.80	$59.80
Purchase #6	$93.48	13.255%	$105.8708	$105.87	$105.85	$105.90
Purchase #7	$88.88	7.432%	$95.4856	$95.49	$95.50	$95.50
7 purchase totals =	$786.26		$840.5885	$840.59	$840.55	$840.60