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	$149.34	12.674%	$168.2674	$168.27	$168.25	$168.30
Purchase #2	$125.98	13.796%	$143.3602	$143.36	$143.35	$143.40
Purchase #3	$83.52	9.553%	$91.4987	$91.50	$91.50	$91.50
Purchase #4	$43.28	5.336%	$45.5894	$45.59	$45.60	$45.60
Purchase #5	$171.28	12.866%	$193.3169	$193.32	$193.30	$193.30
Purchase #6	$81.61	10.850%	$90.4647	$90.46	$90.45	$90.50
Purchase #7	$87.80	6.548%	$93.5491	$93.55	$93.55	$93.50
7 purchase totals =	$742.81		$826.0464	$826.05	$826.00	$826.10