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	$36.44	9.665%	$39.9619	$39.96	$39.95	$40.00
Purchase #2	$179.41	11.108%	$199.3389	$199.34	$199.35	$199.30
Purchase #3	$172.31	11.340%	$191.85	$191.85	$191.85	$191.90
Purchase #4	$21.77	12.422%	$24.4743	$24.47	$24.45	$24.50
Purchase #5	$222.55	4.528%	$232.6271	$232.63	$232.65	$232.60
Purchase #6	$59.38	12.484%	$66.793	$66.79	$66.80	$66.80
Purchase #7	$231.83	4.549%	$242.3759	$242.38	$242.40	$242.40
7 purchase totals =	$923.69		$997.4211	$997.42	$997.45	$997.50