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	$243.29	5.289%	$256.1576	$256.16	$256.15	$256.20
Purchase #2	$140.52	6.824%	$150.1091	$150.11	$150.10	$150.10
Purchase #3	$125.85	13.859%	$143.2916	$143.29	$143.30	$143.30
Purchase #4	$231.52	10.603%	$256.0681	$256.07	$256.05	$256.10
Purchase #5	$98.56	11.181%	$109.58	$109.58	$109.60	$109.60
Purchase #6	$41.71	11.230%	$46.394	$46.39	$46.40	$46.40
Purchase #7	$27.96	9.603%	$30.645	$30.65	$30.65	$30.60
7 purchase totals =	$909.41		$992.2454	$992.25	$992.25	$992.30