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	$59.51	13.456%	$67.5177	$67.52	$67.50	$67.50
Purchase #2	$156.99	6.610%	$167.367	$167.37	$167.35	$167.40
Purchase #3	$226.56	13.733%	$257.6735	$257.67	$257.65	$257.70
Purchase #4	$35.46	5.808%	$37.5195	$37.52	$37.50	$37.50
Purchase #5	$100.90	7.618%	$108.5866	$108.59	$108.60	$108.60
Purchase #6	$122.79	12.785%	$138.4887	$138.49	$138.50	$138.50
Purchase #7	$197.40	11.103%	$219.3173	$219.32	$219.30	$219.30
7 purchase totals =	$899.61		$996.4703	$996.48	$996.40	$996.50