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	$100.62	7.816%	$108.4845	$108.48	$108.50	$108.50
Purchase #2	$152.55	13.222%	$172.7202	$172.72	$172.70	$172.70
Purchase #3	$99.56	12.355%	$111.8606	$111.86	$111.85	$111.90
Purchase #4	$224.52	10.405%	$247.8813	$247.88	$247.90	$247.90
Purchase #5	$113.83	11.387%	$126.7918	$126.79	$126.80	$126.80
Purchase #6	$199.45	4.688%	$208.8002	$208.80	$208.80	$208.80
Purchase #7	$223.78	8.756%	$243.3742	$243.37	$243.35	$243.40
7 purchase totals =	$1,114.31		$1,219.9128	$1,219.90	$1,219.90	$1,220.00