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	$21.90	3.134%	$22.5863	$22.59	$22.60	$22.60
Purchase #2	$89.62	11.429%	$99.8627	$99.86	$99.85	$99.90
Purchase #3	$116.38	5.733%	$123.0521	$123.05	$123.05	$123.10
Purchase #4	$48.87	9.767%	$53.6431	$53.64	$53.65	$53.60
Purchase #5	$85.40	11.319%	$95.0664	$95.07	$95.05	$95.10
Purchase #6	$32.57	7.356%	$34.9658	$34.97	$34.95	$35.00
Purchase #7	$92.79	3.287%	$95.84	$95.84	$95.85	$95.80
7 purchase totals =	$487.53		$525.0164	$525.02	$525.00	$525.10