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	$180.94	13.729%	$205.7813	$205.78	$205.80	$205.80
Purchase #2	$182.69	9.827%	$200.6429	$200.64	$200.65	$200.60
Purchase #3	$133.59	11.849%	$149.4191	$149.42	$149.40	$149.40
Purchase #4	$50.53	4.761%	$52.9357	$52.94	$52.95	$52.90
Purchase #5	$34.89	13.600%	$39.635	$39.64	$39.65	$39.60
Purchase #6	$132.60	3.214%	$136.8618	$136.86	$136.85	$136.90
Purchase #7	$209.78	3.873%	$217.9048	$217.90	$217.90	$217.90
7 purchase totals =	$925.02		$1,003.1806	$1,003.18	$1,003.20	$1,003.10