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	$166.63	13.761%	$189.56	$189.56	$189.55	$189.60
Purchase #2	$31.42	10.665%	$34.7709	$34.77	$34.75	$34.80
Purchase #3	$213.67	6.751%	$228.0949	$228.09	$228.10	$228.10
Purchase #4	$46.79	5.524%	$49.3747	$49.37	$49.35	$49.40
Purchase #5	$81.79	8.864%	$89.0399	$89.04	$89.05	$89.00
Purchase #6	$59.81	7.151%	$64.087	$64.09	$64.10	$64.10
Purchase #7	$66.63	7.401%	$71.5613	$71.56	$71.55	$71.60
7 purchase totals =	$666.74		$726.4887	$726.48	$726.45	$726.60