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	$17.34	6.587%	$18.4822	$18.48	$18.50	$18.50
Purchase #2	$82.83	6.540%	$88.2471	$88.25	$88.25	$88.20
Purchase #3	$55.31	13.573%	$62.8172	$62.82	$62.80	$62.80
Purchase #4	$49.55	10.338%	$54.6725	$54.67	$54.65	$54.70
Purchase #5	$8.90	12.143%	$9.9807	$9.98	$10.00	$10.00
Purchase #6	$21.62	10.676%	$23.9282	$23.93	$23.95	$23.90
Purchase #7	$55.78	10.723%	$61.7613	$61.76	$61.75	$61.80
7 purchase totals =	$291.33		$319.8892	$319.89	$319.90	$319.90