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	$33.52	12.418%	$37.6825	$37.68	$37.70	$37.70
Purchase #2	$113.61	10.689%	$125.7538	$125.75	$125.75	$125.80
Purchase #3	$32.82	10.678%	$36.3245	$36.32	$36.30	$36.30
Purchase #4	$103.29	8.285%	$111.8476	$111.85	$111.85	$111.80
Purchase #5	$240.30	9.238%	$262.4989	$262.50	$262.50	$262.50
Purchase #6	$152.80	8.257%	$165.4167	$165.42	$165.40	$165.40
Purchase #7	$85.71	10.431%	$94.6504	$94.65	$94.65	$94.70
7 purchase totals =	$762.05		$834.1744	$834.17	$834.15	$834.20