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	$109.46	6.431%	$116.4994	$116.50	$116.50	$116.50
Purchase #2	$138.69	4.540%	$144.9865	$144.99	$145.00	$145.00
Purchase #3	$134.66	12.352%	$151.2932	$151.29	$151.30	$151.30
Purchase #4	$30.39	13.855%	$34.6005	$34.60	$34.60	$34.60
Purchase #5	$76.85	4.721%	$80.4781	$80.48	$80.50	$80.50
Purchase #6	$129.35	10.395%	$142.7959	$142.80	$142.80	$142.80
Purchase #7	$170.47	11.339%	$189.7996	$189.80	$189.80	$189.80
7 purchase totals =	$789.87		$860.4532	$860.46	$860.50	$860.50