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	$239.90	8.874%	$261.1887	$261.19	$261.20	$261.20
Purchase #2	$59.78	11.263%	$66.513	$66.51	$66.50	$66.50
Purchase #3	$144.83	12.510%	$162.9482	$162.95	$162.95	$162.90
Purchase #4	$44.82	6.794%	$47.8651	$47.87	$47.85	$47.90
Purchase #5	$40.50	9.693%	$44.4257	$44.43	$44.45	$44.40
Purchase #6	$136.68	13.497%	$155.1277	$155.13	$155.15	$155.10
Purchase #7	$89.82	3.408%	$92.8811	$92.88	$92.90	$92.90
7 purchase totals =	$756.33		$830.9495	$830.96	$831.00	$830.90