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	$52.55	8.295%	$56.909	$56.91	$56.90	$56.90
Purchase #2	$126.89	8.171%	$137.2582	$137.26	$137.25	$137.30
Purchase #3	$218.28	11.441%	$243.2534	$243.25	$243.25	$243.30
Purchase #4	$41.46	8.369%	$44.9298	$44.93	$44.95	$44.90
Purchase #5	$92.32	3.441%	$95.4967	$95.50	$95.50	$95.50
Purchase #6	$39.76	9.441%	$43.5137	$43.51	$43.50	$43.50
Purchase #7	$27.27	9.792%	$29.9403	$29.94	$29.95	$29.90
7 purchase totals =	$598.53		$651.3011	$651.30	$651.30	$651.30