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	$77.51	6.288%	$82.3838	$82.38	$82.40	$82.40
Purchase #2	$125.77	13.859%	$143.2005	$143.20	$143.20	$143.20
Purchase #3	$162.40	10.140%	$178.8674	$178.87	$178.85	$178.90
Purchase #4	$45.94	11.215%	$51.0922	$51.09	$51.10	$51.10
Purchase #5	$240.29	8.309%	$260.2557	$260.26	$260.25	$260.30
Purchase #6	$148.32	10.749%	$164.2629	$164.26	$164.25	$164.30
Purchase #7	$7.63	3.729%	$7.9145	$7.91	$7.90	$7.90
7 purchase totals =	$807.86		$887.9770	$887.97	$887.95	$888.10