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	$216.39	7.167%	$231.8987	$231.90	$231.90	$231.90
Purchase #2	$74.36	9.616%	$81.5105	$81.51	$81.50	$81.50
Purchase #3	$104.79	12.326%	$117.7064	$117.71	$117.70	$117.70
Purchase #4	$92.89	11.863%	$103.9095	$103.91	$103.90	$103.90
Purchase #5	$221.90	8.710%	$241.2275	$241.23	$241.25	$241.20
Purchase #6	$198.27	7.624%	$213.3861	$213.39	$213.40	$213.40
Purchase #7	$137.56	12.160%	$154.2873	$154.29	$154.30	$154.30
7 purchase totals =	$1,046.16		$1,143.9260	$1,143.94	$1,143.95	$1,143.90