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	$107.74	13.128%	$121.8841	$121.88	$121.90	$121.90
Purchase #2	$167.38	3.471%	$173.1898	$173.19	$173.20	$173.20
Purchase #3	$35.32	13.507%	$40.0907	$40.09	$40.10	$40.10
Purchase #4	$167.61	3.631%	$173.6959	$173.70	$173.70	$173.70
Purchase #5	$53.41	11.464%	$59.5329	$59.53	$59.55	$59.50
Purchase #6	$213.57	11.661%	$238.4744	$238.47	$238.45	$238.50
Purchase #7	$111.37	8.246%	$120.5536	$120.55	$120.55	$120.60
7 purchase totals =	$856.40		$927.4214	$927.41	$927.45	$927.50