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	$24.54	11.727%	$27.4178	$27.42	$27.40	$27.40
Purchase #2	$225.98	6.128%	$239.8281	$239.83	$239.85	$239.80
Purchase #3	$143.82	12.669%	$162.0406	$162.04	$162.05	$162.00
Purchase #4	$54.49	8.698%	$59.2295	$59.23	$59.25	$59.20
Purchase #5	$157.67	9.459%	$172.584	$172.58	$172.60	$172.60
Purchase #6	$169.66	12.483%	$190.8387	$190.84	$190.85	$190.80
Purchase #7	$140.51	11.671%	$156.9089	$156.91	$156.90	$156.90
7 purchase totals =	$916.67		$1,008.8476	$1,008.85	$1,008.90	$1,008.70