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	$128.33	7.501%	$137.956	$137.96	$137.95	$138.00
Purchase #2	$44.82	9.398%	$49.0322	$49.03	$49.05	$49.00
Purchase #3	$48.44	8.383%	$52.5007	$52.50	$52.50	$52.50
Purchase #4	$31.98	9.268%	$34.9439	$34.94	$34.95	$34.90
Purchase #5	$61.72	7.718%	$66.4835	$66.48	$66.50	$66.50
Purchase #6	$92.89	12.308%	$104.3229	$104.32	$104.30	$104.30
Purchase #7	$95.87	7.734%	$103.2846	$103.28	$103.30	$103.30
7 purchase totals =	$504.05		$548.5238	$548.51	$548.55	$548.50