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	$97.74	4.198%	$101.8431	$101.84	$101.85	$101.80
Purchase #2	$232.94	7.758%	$251.0115	$251.01	$251.00	$251.00
Purchase #3	$83.82	7.813%	$90.3689	$90.37	$90.35	$90.40
Purchase #4	$118.80	10.795%	$131.6245	$131.62	$131.60	$131.60
Purchase #5	$128.67	11.193%	$143.072	$143.07	$143.05	$143.10
Purchase #6	$43.72	12.626%	$49.2401	$49.24	$49.25	$49.20
Purchase #7	$20.53	9.513%	$22.483	$22.48	$22.50	$22.50
7 purchase totals =	$726.22		$789.6431	$789.63	$789.60	$789.60