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	$117.39	4.360%	$122.5082	$122.51	$122.50	$122.50
Purchase #2	$112.38	13.464%	$127.5108	$127.51	$127.50	$127.50
Purchase #3	$244.99	10.865%	$271.6082	$271.61	$271.60	$271.60
Purchase #4	$120.96	7.511%	$130.0453	$130.05	$130.05	$130.00
Purchase #5	$80.26	8.181%	$86.8261	$86.83	$86.85	$86.80
Purchase #6	$150.54	11.189%	$167.3839	$167.38	$167.40	$167.40
Purchase #7	$118.51	5.863%	$125.4582	$125.46	$125.45	$125.50
7 purchase totals =	$945.03		$1,031.3407	$1,031.35	$1,031.35	$1,031.30