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	$30.34	6.275%	$32.2438	$32.24	$32.25	$32.20
Purchase #2	$123.73	7.102%	$132.5173	$132.52	$132.50	$132.50
Purchase #3	$102.91	13.383%	$116.6824	$116.68	$116.70	$116.70
Purchase #4	$131.96	11.376%	$146.9718	$146.97	$146.95	$147.00
Purchase #5	$97.46	3.505%	$100.876	$100.88	$100.90	$100.90
Purchase #6	$30.72	10.801%	$34.0381	$34.04	$34.05	$34.00
Purchase #7	$168.82	4.757%	$176.8508	$176.85	$176.85	$176.90
7 purchase totals =	$685.94		$740.1802	$740.18	$740.20	$740.20