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	$223.66	12.503%	$251.6242	$251.62	$251.60	$251.60
Purchase #2	$37.39	8.309%	$40.4967	$40.50	$40.50	$40.50
Purchase #3	$72.38	5.202%	$76.1452	$76.15	$76.15	$76.10
Purchase #4	$203.71	8.468%	$220.9602	$220.96	$220.95	$221.00
Purchase #5	$157.42	5.239%	$165.6672	$165.67	$165.65	$165.70
Purchase #6	$45.64	9.564%	$50.005	$50.01	$50.00	$50.00
Purchase #7	$154.42	12.623%	$173.9124	$173.91	$173.90	$173.90
7 purchase totals =	$894.62		$978.8109	$978.82	$978.75	$978.80