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	$223.35	13.391%	$253.2588	$253.26	$253.25	$253.30
Purchase #2	$243.72	12.724%	$274.7309	$274.73	$274.75	$274.70
Purchase #3	$121.33	12.766%	$136.819	$136.82	$136.80	$136.80
Purchase #4	$50.71	10.518%	$56.0437	$56.04	$56.05	$56.00
Purchase #5	$102.38	3.106%	$105.5599	$105.56	$105.55	$105.60
Purchase #6	$58.29	3.630%	$60.4059	$60.41	$60.40	$60.40
Purchase #7	$37.93	6.581%	$40.4262	$40.43	$40.45	$40.40
7 purchase totals =	$837.71		$927.2444	$927.25	$927.25	$927.20