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	$70.92	11.259%	$78.9049	$78.90	$78.90	$78.90
Purchase #2	$188.77	3.584%	$195.5355	$195.54	$195.55	$195.50
Purchase #3	$32.66	4.622%	$34.1695	$34.17	$34.15	$34.20
Purchase #4	$20.71	4.113%	$21.5618	$21.56	$21.55	$21.60
Purchase #5	$6.78	13.470%	$7.6933	$7.69	$7.70	$7.70
Purchase #6	$227.86	3.355%	$235.5047	$235.50	$235.50	$235.50
Purchase #7	$247.89	3.466%	$256.4819	$256.48	$256.50	$256.50
7 purchase totals =	$795.59		$829.8516	$829.84	$829.85	$829.90