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	$108.48	13.710%	$123.3526	$123.35	$123.35	$123.40
Purchase #2	$44.94	9.306%	$49.1221	$49.12	$49.10	$49.10
Purchase #3	$50.86	10.406%	$56.1525	$56.15	$56.15	$56.20
Purchase #4	$83.45	8.482%	$90.5282	$90.53	$90.55	$90.50
Purchase #5	$221.71	4.384%	$231.4298	$231.43	$231.45	$231.40
Purchase #6	$52.49	12.261%	$58.9258	$58.93	$58.95	$58.90
Purchase #7	$233.42	12.210%	$261.9206	$261.92	$261.90	$261.90
7 purchase totals =	$795.35		$871.4316	$871.43	$871.45	$871.40