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	$208.60	13.262%	$236.2645	$236.26	$236.25	$236.30
Purchase #2	$141.56	6.283%	$150.4542	$150.45	$150.45	$150.50
Purchase #3	$52.85	12.803%	$59.6164	$59.62	$59.60	$59.60
Purchase #4	$144.96	5.259%	$152.5834	$152.58	$152.60	$152.60
Purchase #5	$71.30	7.340%	$76.5334	$76.53	$76.55	$76.50
Purchase #6	$208.96	9.482%	$228.7736	$228.77	$228.75	$228.80
Purchase #7	$44.41	3.597%	$46.0074	$46.01	$46.00	$46.00
7 purchase totals =	$872.64		$950.2329	$950.22	$950.20	$950.30