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	$239.81	13.787%	$272.8726	$272.87	$272.85	$272.90
Purchase #2	$40.98	3.507%	$42.4172	$42.42	$42.40	$42.40
Purchase #3	$51.36	7.540%	$55.2325	$55.23	$55.25	$55.20
Purchase #4	$69.47	11.504%	$77.4618	$77.46	$77.45	$77.50
Purchase #5	$98.83	5.759%	$104.5216	$104.52	$104.50	$104.50
Purchase #6	$242.77	3.310%	$250.8057	$250.81	$250.80	$250.80
Purchase #7	$109.68	3.636%	$113.668	$113.67	$113.65	$113.70
7 purchase totals =	$852.90		$916.9794	$916.98	$916.90	$917.00