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	$28.47	13.334%	$32.2662	$32.27	$32.25	$32.30
Purchase #2	$178.87	12.181%	$200.6582	$200.66	$200.65	$200.70
Purchase #3	$157.84	12.422%	$177.4469	$177.45	$177.45	$177.40
Purchase #4	$78.77	5.750%	$83.2993	$83.30	$83.30	$83.30
Purchase #5	$228.67	7.189%	$245.1091	$245.11	$245.10	$245.10
Purchase #6	$82.34	10.181%	$90.723	$90.72	$90.70	$90.70
Purchase #7	$231.63	9.288%	$253.1438	$253.14	$253.15	$253.10
7 purchase totals =	$986.59		$1,082.6465	$1,082.65	$1,082.60	$1,082.60