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	$35.89	10.447%	$39.6394	$39.64	$39.65	$39.60
Purchase #2	$92.71	11.812%	$103.6609	$103.66	$103.65	$103.70
Purchase #3	$35.82	6.605%	$38.1859	$38.19	$38.20	$38.20
Purchase #4	$135.95	6.626%	$144.958	$144.96	$144.95	$145.00
Purchase #5	$209.76	3.305%	$216.6926	$216.69	$216.70	$216.70
Purchase #6	$41.73	9.176%	$45.5591	$45.56	$45.55	$45.60
Purchase #7	$248.98	12.509%	$280.1249	$280.12	$280.10	$280.10
7 purchase totals =	$800.84		$868.8208	$868.82	$868.80	$868.90