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	$40.78	7.640%	$43.8956	$43.90	$43.90	$43.90
Purchase #2	$27.95	12.495%	$31.4424	$31.44	$31.45	$31.40
Purchase #3	$128.61	13.143%	$145.5132	$145.51	$145.50	$145.50
Purchase #4	$200.73	9.675%	$220.1506	$220.15	$220.15	$220.20
Purchase #5	$227.42	6.325%	$241.8043	$241.80	$241.80	$241.80
Purchase #6	$84.29	7.335%	$90.4727	$90.47	$90.45	$90.50
Purchase #7	$146.95	8.461%	$159.3834	$159.38	$159.40	$159.40
7 purchase totals =	$856.73		$932.6622	$932.65	$932.65	$932.70