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	$133.60	3.169%	$137.8338	$137.83	$137.85	$137.80
Purchase #2	$231.53	4.840%	$242.7361	$242.74	$242.75	$242.70
Purchase #3	$200.43	10.505%	$221.4852	$221.49	$221.50	$221.50
Purchase #4	$75.37	10.575%	$83.3404	$83.34	$83.35	$83.30
Purchase #5	$132.71	4.800%	$139.0801	$139.08	$139.10	$139.10
Purchase #6	$239.85	7.866%	$258.7166	$258.72	$258.70	$258.70
Purchase #7	$36.40	12.237%	$40.8543	$40.85	$40.85	$40.90
7 purchase totals =	$1,049.89		$1,124.0465	$1,124.05	$1,124.10	$1,124.00