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	$64.39	12.117%	$72.1921	$72.19	$72.20	$72.20
Purchase #2	$152.40	4.646%	$159.4805	$159.48	$159.50	$159.50
Purchase #3	$211.51	12.769%	$238.5177	$238.52	$238.50	$238.50
Purchase #4	$20.41	6.105%	$21.656	$21.66	$21.65	$21.70
Purchase #5	$165.89	11.126%	$184.3469	$184.35	$184.35	$184.30
Purchase #6	$74.35	13.644%	$84.4943	$84.49	$84.50	$84.50
Purchase #7	$125.26	13.561%	$142.2465	$142.25	$142.25	$142.20
7 purchase totals =	$814.21		$902.9340	$902.94	$902.95	$902.90