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	$74.83	11.600%	$83.5103	$83.51	$83.50	$83.50
Purchase #2	$214.28	12.648%	$241.3821	$241.38	$241.40	$241.40
Purchase #3	$138.39	12.728%	$156.0043	$156.00	$156.00	$156.00
Purchase #4	$112.25	3.826%	$116.5447	$116.54	$116.55	$116.50
Purchase #5	$225.51	9.243%	$246.3539	$246.35	$246.35	$246.40
Purchase #6	$17.73	6.514%	$18.8849	$18.88	$18.90	$18.90
Purchase #7	$113.72	5.121%	$119.5436	$119.54	$119.55	$119.50
7 purchase totals =	$896.71		$982.2238	$982.20	$982.25	$982.20