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	$37.37	13.850%	$42.5457	$42.55	$42.55	$42.50
Purchase #2	$203.78	10.178%	$224.5207	$224.52	$224.50	$224.50
Purchase #3	$93.63	13.429%	$106.2036	$106.20	$106.20	$106.20
Purchase #4	$10.79	6.702%	$11.5131	$11.51	$11.50	$11.50
Purchase #5	$132.98	13.167%	$150.4895	$150.49	$150.50	$150.50
Purchase #6	$94.74	5.648%	$100.0909	$100.09	$100.10	$100.10
Purchase #7	$234.44	10.836%	$259.8439	$259.84	$259.85	$259.80
7 purchase totals =	$807.73		$895.2074	$895.20	$895.20	$895.10