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	$33.54	11.841%	$37.5115	$37.51	$37.50	$37.50
Purchase #2	$80.94	5.616%	$85.4856	$85.49	$85.50	$85.50
Purchase #3	$230.77	12.663%	$259.9924	$259.99	$260.00	$260.00
Purchase #4	$47.51	11.551%	$52.9979	$53.00	$53.00	$53.00
Purchase #5	$169.71	12.407%	$190.7659	$190.77	$190.75	$190.80
Purchase #6	$231.50	7.749%	$249.4389	$249.44	$249.45	$249.40
Purchase #7	$93.29	7.733%	$100.5041	$100.50	$100.50	$100.50
7 purchase totals =	$887.26		$976.6963	$976.70	$976.70	$976.70