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	$68.94	5.177%	$72.509	$72.51	$72.50	$72.50
Purchase #2	$144.30	8.537%	$156.6189	$156.62	$156.60	$156.60
Purchase #3	$30.87	7.493%	$33.1831	$33.18	$33.20	$33.20
Purchase #4	$249.72	5.204%	$262.7154	$262.72	$262.70	$262.70
Purchase #5	$110.46	13.556%	$125.434	$125.43	$125.45	$125.40
Purchase #6	$48.34	4.637%	$50.5815	$50.58	$50.60	$50.60
Purchase #7	$117.26	11.621%	$130.8868	$130.89	$130.90	$130.90
7 purchase totals =	$769.89		$831.9287	$831.93	$831.95	$831.90