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	$42.51	10.662%	$47.0424	$47.04	$47.05	$47.00
Purchase #2	$94.54	9.589%	$103.6054	$103.61	$103.60	$103.60
Purchase #3	$237.34	5.341%	$250.0163	$250.02	$250.00	$250.00
Purchase #4	$120.48	10.285%	$132.8714	$132.87	$132.85	$132.90
Purchase #5	$37.50	4.249%	$39.0934	$39.09	$39.10	$39.10
Purchase #6	$109.75	3.650%	$113.7559	$113.76	$113.75	$113.80
Purchase #7	$23.77	4.836%	$24.9195	$24.92	$24.90	$24.90
7 purchase totals =	$665.89		$711.3043	$711.31	$711.25	$711.30