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	$92.83	13.298%	$105.1745	$105.17	$105.15	$105.20
Purchase #2	$130.65	5.257%	$137.5183	$137.52	$137.50	$137.50
Purchase #3	$75.38	8.825%	$82.0323	$82.03	$82.05	$82.00
Purchase #4	$51.29	11.674%	$57.2776	$57.28	$57.30	$57.30
Purchase #5	$198.52	4.858%	$208.1641	$208.16	$208.15	$208.20
Purchase #6	$131.81	13.197%	$149.205	$149.21	$149.20	$149.20
Purchase #7	$105.45	3.859%	$109.5193	$109.52	$109.50	$109.50
7 purchase totals =	$785.93		$848.8911	$848.89	$848.85	$848.90