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	$41.31	8.678%	$44.8949	$44.89	$44.90	$44.90
Purchase #2	$188.62	13.222%	$213.5593	$213.56	$213.55	$213.60
Purchase #3	$133.47	6.167%	$141.7011	$141.70	$141.70	$141.70
Purchase #4	$169.97	12.137%	$190.5993	$190.60	$190.60	$190.60
Purchase #5	$34.51	12.490%	$38.8203	$38.82	$38.80	$38.80
Purchase #6	$87.63	5.873%	$92.7765	$92.78	$92.80	$92.80
Purchase #7	$59.25	10.516%	$65.4807	$65.48	$65.50	$65.50
7 purchase totals =	$714.76		$787.8321	$787.83	$787.85	$787.90