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	$74.83	4.332%	$78.0716	$78.07	$78.05	$78.10
Purchase #2	$108.67	9.733%	$119.2469	$119.25	$119.25	$119.20
Purchase #3	$197.39	8.530%	$214.2274	$214.23	$214.25	$214.20
Purchase #4	$218.37	10.294%	$240.849	$240.85	$240.85	$240.80
Purchase #5	$180.68	4.686%	$189.1467	$189.15	$189.15	$189.10
Purchase #6	$45.61	13.763%	$51.8873	$51.89	$51.90	$51.90
Purchase #7	$37.39	5.541%	$39.4618	$39.46	$39.45	$39.50
7 purchase totals =	$862.94		$932.8907	$932.90	$932.90	$932.80