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	$173.85	5.174%	$182.845	$182.85	$182.85	$182.80
Purchase #2	$133.64	11.142%	$148.5302	$148.53	$148.55	$148.50
Purchase #3	$129.45	10.846%	$143.4901	$143.49	$143.50	$143.50
Purchase #4	$40.79	4.682%	$42.6998	$42.70	$42.70	$42.70
Purchase #5	$48.59	8.442%	$52.692	$52.69	$52.70	$52.70
Purchase #6	$153.89	11.135%	$171.0257	$171.03	$171.05	$171.00
Purchase #7	$88.69	7.123%	$95.0074	$95.01	$95.00	$95.00
7 purchase totals =	$768.90		$836.2902	$836.30	$836.35	$836.20