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	$208.43	8.344%	$225.8214	$225.82	$225.80	$225.80
Purchase #2	$231.43	5.277%	$243.6426	$243.64	$243.65	$243.60
Purchase #3	$106.74	4.195%	$111.2177	$111.22	$111.20	$111.20
Purchase #4	$105.78	7.240%	$113.4385	$113.44	$113.45	$113.40
Purchase #5	$39.87	4.168%	$41.5318	$41.53	$41.55	$41.50
Purchase #6	$100.81	4.364%	$105.2093	$105.21	$105.20	$105.20
Purchase #7	$139.89	7.596%	$150.516	$150.52	$150.50	$150.50
7 purchase totals =	$932.95		$991.3773	$991.38	$991.35	$991.20