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	$216.33	3.585%	$224.0854	$224.09	$224.10	$224.10
Purchase #2	$222.89	12.750%	$251.3085	$251.31	$251.30	$251.30
Purchase #3	$249.42	8.612%	$270.9001	$270.90	$270.90	$270.90
Purchase #4	$28.65	13.669%	$32.5662	$32.57	$32.55	$32.60
Purchase #5	$37.43	7.614%	$40.2799	$40.28	$40.30	$40.30
Purchase #6	$80.55	3.745%	$83.5666	$83.57	$83.55	$83.60
Purchase #7	$66.85	8.470%	$72.5122	$72.51	$72.50	$72.50
7 purchase totals =	$902.12		$975.2189	$975.23	$975.20	$975.30