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	$83.69	6.447%	$89.0855	$89.09	$89.10	$89.10
Purchase #2	$162.80	8.166%	$176.0942	$176.09	$176.10	$176.10
Purchase #3	$138.32	12.704%	$155.8922	$155.89	$155.90	$155.90
Purchase #4	$97.46	6.582%	$103.8748	$103.87	$103.85	$103.90
Purchase #5	$103.32	8.440%	$112.0402	$112.04	$112.05	$112.00
Purchase #6	$48.51	11.824%	$54.2458	$54.25	$54.25	$54.20
Purchase #7	$13.32	9.411%	$14.5735	$14.57	$14.55	$14.60
7 purchase totals =	$647.42		$705.8062	$705.80	$705.80	$705.80