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	$219.89	6.192%	$233.5056	$233.51	$233.50	$233.50
Purchase #2	$215.49	4.414%	$225.0017	$225.00	$225.00	$225.00
Purchase #3	$31.87	7.503%	$34.2612	$34.26	$34.25	$34.30
Purchase #4	$14.36	10.568%	$15.8776	$15.88	$15.90	$15.90
Purchase #5	$51.98	7.750%	$56.0085	$56.01	$56.00	$56.00
Purchase #6	$38.27	13.186%	$43.3163	$43.32	$43.30	$43.30
Purchase #7	$88.87	13.533%	$100.8968	$100.90	$100.90	$100.90
7 purchase totals =	$660.73		$708.8677	$708.88	$708.85	$708.90