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	$131.87	6.382%	$140.2859	$140.29	$140.30	$140.30
Purchase #2	$178.90	11.514%	$199.4985	$199.50	$199.50	$199.50
Purchase #3	$37.67	10.700%	$41.7007	$41.70	$41.70	$41.70
Purchase #4	$161.68	4.830%	$169.4891	$169.49	$169.50	$169.50
Purchase #5	$174.34	12.519%	$196.1656	$196.17	$196.15	$196.20
Purchase #6	$11.89	12.831%	$13.4156	$13.42	$13.40	$13.40
Purchase #7	$56.44	9.564%	$61.8379	$61.84	$61.85	$61.80
7 purchase totals =	$752.79		$822.3933	$822.41	$822.40	$822.40