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	$33.34	12.725%	$37.5825	$37.58	$37.60	$37.60
Purchase #2	$134.51	12.154%	$150.8583	$150.86	$150.85	$150.90
Purchase #3	$108.42	7.406%	$116.4496	$116.45	$116.45	$116.40
Purchase #4	$250.95	11.379%	$279.5056	$279.51	$279.50	$279.50
Purchase #5	$147.80	6.540%	$157.4661	$157.47	$157.45	$157.50
Purchase #6	$156.40	7.260%	$167.7546	$167.75	$167.75	$167.80
Purchase #7	$6.77	10.850%	$7.5045	$7.50	$7.50	$7.50
7 purchase totals =	$838.19		$917.1212	$917.12	$917.10	$917.20