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	$76.60	12.277%	$86.0042	$86.00	$86.00	$86.00
Purchase #2	$99.85	5.695%	$105.5365	$105.54	$105.55	$105.50
Purchase #3	$40.90	10.426%	$45.1642	$45.16	$45.15	$45.20
Purchase #4	$121.93	13.515%	$138.4088	$138.41	$138.40	$138.40
Purchase #5	$82.41	5.198%	$86.6937	$86.69	$86.70	$86.70
Purchase #6	$29.82	5.582%	$31.4846	$31.48	$31.50	$31.50
Purchase #7	$178.42	6.646%	$190.2778	$190.28	$190.30	$190.30
7 purchase totals =	$629.93		$683.5698	$683.56	$683.60	$683.60