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	$21.51	12.527%	$24.2046	$24.20	$24.20	$24.20
Purchase #2	$88.89	3.438%	$91.946	$91.95	$91.95	$91.90
Purchase #3	$153.59	4.750%	$160.8855	$160.89	$160.90	$160.90
Purchase #4	$136.37	6.340%	$145.0159	$145.02	$145.00	$145.00
Purchase #5	$65.53	11.177%	$72.8543	$72.85	$72.85	$72.90
Purchase #6	$77.94	10.411%	$86.0543	$86.05	$86.05	$86.10
Purchase #7	$183.96	4.626%	$192.47	$192.47	$192.45	$192.50
7 purchase totals =	$727.79		$773.4306	$773.43	$773.40	$773.50