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	$37.38	9.404%	$40.8952	$40.90	$40.90	$40.90
Purchase #2	$33.42	13.760%	$38.0186	$38.02	$38.00	$38.00
Purchase #3	$126.62	10.162%	$139.4871	$139.49	$139.50	$139.50
Purchase #4	$168.42	12.160%	$188.8999	$188.90	$188.90	$188.90
Purchase #5	$60.87	9.822%	$66.8487	$66.85	$66.85	$66.80
Purchase #6	$148.96	13.117%	$168.4991	$168.50	$168.50	$168.50
Purchase #7	$34.39	10.703%	$38.0708	$38.07	$38.05	$38.10
7 purchase totals =	$610.06		$680.7194	$680.73	$680.70	$680.70