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	$24.82	8.383%	$26.9007	$26.90	$26.90	$26.90
Purchase #2	$151.92	9.616%	$166.5286	$166.53	$166.55	$166.50
Purchase #3	$149.34	3.454%	$154.4982	$154.50	$154.50	$154.50
Purchase #4	$97.35	3.464%	$100.7222	$100.72	$100.70	$100.70
Purchase #5	$44.40	3.454%	$45.9336	$45.93	$45.95	$45.90
Purchase #6	$244.35	11.516%	$272.4893	$272.49	$272.50	$272.50
Purchase #7	$201.72	10.494%	$222.8885	$222.89	$222.90	$222.90
7 purchase totals =	$913.90		$989.9611	$989.96	$990.00	$989.90