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	$63.93	3.197%	$65.9738	$65.97	$65.95	$66.00
Purchase #2	$53.30	10.354%	$58.8187	$58.82	$58.80	$58.80
Purchase #3	$150.72	11.672%	$168.312	$168.31	$168.30	$168.30
Purchase #4	$39.61	11.806%	$44.2864	$44.29	$44.30	$44.30
Purchase #5	$99.79	11.245%	$111.0114	$111.01	$111.00	$111.00
Purchase #6	$122.65	9.583%	$134.4035	$134.40	$134.40	$134.40
Purchase #7	$243.38	5.174%	$255.9725	$255.97	$255.95	$256.00
7 purchase totals =	$773.38		$838.7783	$838.77	$838.70	$838.80