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	$71.37	10.105%	$78.5819	$78.58	$78.60	$78.60
Purchase #2	$226.54	7.422%	$243.3538	$243.35	$243.35	$243.40
Purchase #3	$197.94	9.554%	$216.8512	$216.85	$216.85	$216.90
Purchase #4	$93.59	11.331%	$104.1947	$104.19	$104.20	$104.20
Purchase #5	$138.44	10.325%	$152.7339	$152.73	$152.75	$152.70
Purchase #6	$91.52	7.737%	$98.6009	$98.60	$98.60	$98.60
Purchase #7	$71.28	8.211%	$77.1328	$77.13	$77.15	$77.10
7 purchase totals =	$890.68		$971.4492	$971.43	$971.50	$971.50