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	$101.63	3.162%	$104.8435	$104.84	$104.85	$104.80
Purchase #2	$242.38	11.523%	$270.3094	$270.31	$270.30	$270.30
Purchase #3	$23.90	10.730%	$26.4645	$26.46	$26.45	$26.50
Purchase #4	$63.93	13.365%	$72.4742	$72.47	$72.45	$72.50
Purchase #5	$42.49	6.623%	$45.3041	$45.30	$45.30	$45.30
Purchase #6	$32.45	7.807%	$34.9834	$34.98	$35.00	$35.00
Purchase #7	$13.61	4.587%	$14.2343	$14.23	$14.25	$14.20
7 purchase totals =	$520.39		$568.6134	$568.59	$568.60	$568.60