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	$201.80	13.735%	$229.5172	$229.52	$229.50	$229.50
Purchase #2	$227.67	6.206%	$241.7992	$241.80	$241.80	$241.80
Purchase #3	$164.34	9.507%	$179.9638	$179.96	$179.95	$180.00
Purchase #4	$153.63	11.863%	$171.8551	$171.86	$171.85	$171.90
Purchase #5	$31.33	11.625%	$34.9721	$34.97	$34.95	$35.00
Purchase #6	$118.57	6.685%	$126.4964	$126.50	$126.50	$126.50
Purchase #7	$48.43	13.222%	$54.8334	$54.83	$54.85	$54.80
7 purchase totals =	$945.77		$1,039.4372	$1,039.44	$1,039.40	$1,039.50