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	$81.61	6.836%	$87.1889	$87.19	$87.20	$87.20
Purchase #2	$52.61	3.340%	$54.3672	$54.37	$54.35	$54.40
Purchase #3	$153.55	11.694%	$171.5061	$171.51	$171.50	$171.50
Purchase #4	$208.85	13.739%	$237.5439	$237.54	$237.55	$237.50
Purchase #5	$77.96	6.827%	$83.2823	$83.28	$83.30	$83.30
Purchase #6	$57.47	7.564%	$61.817	$61.82	$61.80	$61.80
Purchase #7	$74.37	10.683%	$82.3149	$82.31	$82.30	$82.30
7 purchase totals =	$706.42		$778.0203	$778.02	$778.00	$778.00