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	$24.95	10.509%	$27.572	$27.57	$27.55	$27.60
Purchase #2	$66.70	5.294%	$70.2311	$70.23	$70.25	$70.20
Purchase #3	$83.53	6.174%	$88.6871	$88.69	$88.70	$88.70
Purchase #4	$164.81	12.785%	$185.881	$185.88	$185.90	$185.90
Purchase #5	$47.82	10.374%	$52.7808	$52.78	$52.80	$52.80
Purchase #6	$226.37	12.208%	$254.0052	$254.01	$254.00	$254.00
Purchase #7	$137.88	7.371%	$148.0431	$148.04	$148.05	$148.00
7 purchase totals =	$752.06		$827.2003	$827.20	$827.25	$827.20