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	$100.63	5.161%	$105.8235	$105.82	$105.80	$105.80
Purchase #2	$80.95	8.466%	$87.8032	$87.80	$87.80	$87.80
Purchase #3	$108.50	5.497%	$114.4642	$114.46	$114.45	$114.50
Purchase #4	$36.64	6.202%	$38.9124	$38.91	$38.90	$38.90
Purchase #5	$26.46	5.243%	$27.8473	$27.85	$27.85	$27.80
Purchase #6	$38.74	6.645%	$41.3143	$41.31	$41.30	$41.30
Purchase #7	$238.81	10.500%	$263.8851	$263.89	$263.90	$263.90
7 purchase totals =	$630.73		$680.0500	$680.04	$680.00	$680.00