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	$241.68	6.709%	$257.8943	$257.89	$257.90	$257.90
Purchase #2	$166.38	12.221%	$186.7133	$186.71	$186.70	$186.70
Purchase #3	$13.86	3.647%	$14.3655	$14.37	$14.35	$14.40
Purchase #4	$137.95	10.454%	$152.3713	$152.37	$152.35	$152.40
Purchase #5	$182.49	4.624%	$190.9283	$190.93	$190.95	$190.90
Purchase #6	$143.78	3.422%	$148.7002	$148.70	$148.70	$148.70
Purchase #7	$84.50	5.802%	$89.4027	$89.40	$89.40	$89.40
7 purchase totals =	$970.64		$1,040.3756	$1,040.37	$1,040.35	$1,040.40