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	$25.87	5.509%	$27.2952	$27.30	$27.30	$27.30
Purchase #2	$34.39	10.295%	$37.9305	$37.93	$37.95	$37.90
Purchase #3	$102.85	8.685%	$111.7825	$111.78	$111.80	$111.80
Purchase #4	$222.64	9.162%	$243.0383	$243.04	$243.05	$243.00
Purchase #5	$38.55	3.620%	$39.9455	$39.95	$39.95	$39.90
Purchase #6	$229.34	4.796%	$240.3391	$240.34	$240.35	$240.30
Purchase #7	$43.53	13.163%	$49.2599	$49.26	$49.25	$49.30
7 purchase totals =	$697.17		$749.5910	$749.60	$749.65	$749.50