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	$52.93	6.683%	$56.4673	$56.47	$56.45	$56.50
Purchase #2	$141.48	3.373%	$146.2521	$146.25	$146.25	$146.30
Purchase #3	$248.71	10.427%	$274.643	$274.64	$274.65	$274.60
Purchase #4	$118.90	12.146%	$133.3416	$133.34	$133.35	$133.30
Purchase #5	$134.30	6.163%	$142.5769	$142.58	$142.60	$142.60
Purchase #6	$45.56	11.766%	$50.9206	$50.92	$50.90	$50.90
Purchase #7	$89.47	9.721%	$98.1674	$98.17	$98.15	$98.20
7 purchase totals =	$831.35		$902.3689	$902.37	$902.35	$902.40