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	$28.71	12.602%	$32.328	$32.33	$32.35	$32.30
Purchase #2	$10.43	11.833%	$11.6642	$11.66	$11.65	$11.70
Purchase #3	$116.52	10.515%	$128.7721	$128.77	$128.75	$128.80
Purchase #4	$77.31	4.558%	$80.8338	$80.83	$80.85	$80.80
Purchase #5	$160.55	5.581%	$169.5103	$169.51	$169.50	$169.50
Purchase #6	$42.83	4.165%	$44.6139	$44.61	$44.60	$44.60
Purchase #7	$86.70	4.843%	$90.8989	$90.90	$90.90	$90.90
7 purchase totals =	$523.05		$558.6212	$558.61	$558.60	$558.60