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	$176.48	13.620%	$200.5166	$200.52	$200.50	$200.50
Purchase #2	$87.94	6.640%	$93.7792	$93.78	$93.80	$93.80
Purchase #3	$45.76	9.109%	$49.9283	$49.93	$49.95	$49.90
Purchase #4	$56.34	4.715%	$58.9964	$59.00	$59.00	$59.00
Purchase #5	$71.55	6.776%	$76.3982	$76.40	$76.40	$76.40
Purchase #6	$231.53	10.141%	$255.0095	$255.01	$255.00	$255.00
Purchase #7	$208.40	6.797%	$222.5649	$222.56	$222.55	$222.60
7 purchase totals =	$878.00		$957.1931	$957.20	$957.20	$957.20