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	$205.59	12.385%	$231.0523	$231.05	$231.05	$231.10
Purchase #2	$57.53	3.387%	$59.4785	$59.48	$59.50	$59.50
Purchase #3	$128.43	12.577%	$144.5826	$144.58	$144.60	$144.60
Purchase #4	$190.89	4.625%	$199.7187	$199.72	$199.70	$199.70
Purchase #5	$127.76	11.666%	$142.6645	$142.66	$142.65	$142.70
Purchase #6	$30.96	6.508%	$32.9749	$32.97	$32.95	$33.00
Purchase #7	$50.39	3.342%	$52.074	$52.07	$52.05	$52.10
7 purchase totals =	$791.55		$862.5455	$862.53	$862.50	$862.70