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	$35.53	13.617%	$40.3681	$40.37	$40.35	$40.40
Purchase #2	$12.63	10.210%	$13.9195	$13.92	$13.90	$13.90
Purchase #3	$45.51	10.406%	$50.2458	$50.25	$50.25	$50.20
Purchase #4	$132.71	13.678%	$150.8621	$150.86	$150.85	$150.90
Purchase #5	$248.34	9.449%	$271.8056	$271.81	$271.80	$271.80
Purchase #6	$83.96	11.821%	$93.8849	$93.88	$93.90	$93.90
Purchase #7	$161.25	6.854%	$172.3021	$172.30	$172.30	$172.30
7 purchase totals =	$719.93		$793.3881	$793.39	$793.35	$793.40