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	$120.86	13.859%	$137.61	$137.61	$137.60	$137.60
Purchase #2	$227.51	13.562%	$258.3649	$258.36	$258.35	$258.40
Purchase #3	$201.28	13.273%	$227.9959	$228.00	$228.00	$228.00
Purchase #4	$83.47	12.497%	$93.9012	$93.90	$93.90	$93.90
Purchase #5	$86.95	10.188%	$95.8085	$95.81	$95.80	$95.80
Purchase #6	$146.31	6.774%	$156.221	$156.22	$156.20	$156.20
Purchase #7	$38.45	9.483%	$42.0962	$42.10	$42.10	$42.10
7 purchase totals =	$904.83		$1,011.9977	$1,012.00	$1,011.95	$1,012.00