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	$48.45	3.758%	$50.2708	$50.27	$50.25	$50.30
Purchase #2	$9.68	9.584%	$10.6077	$10.61	$10.60	$10.60
Purchase #3	$50.48	7.715%	$54.3745	$54.37	$54.35	$54.40
Purchase #4	$189.26	12.381%	$212.6923	$212.69	$212.70	$212.70
Purchase #5	$37.54	7.194%	$40.2406	$40.24	$40.25	$40.20
Purchase #6	$72.64	7.162%	$77.8425	$77.84	$77.85	$77.80
Purchase #7	$42.51	13.724%	$48.3441	$48.34	$48.35	$48.30
7 purchase totals =	$450.56		$494.3725	$494.36	$494.35	$494.30