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 $231.71   13.340%   $262.6201   $262.62   $262.60   $262.60  
  Purchase #2 $129.70   9.393%   $141.8827   $141.88   $141.90   $141.90  
  Purchase #3 $161.53   10.743%   $178.8832   $178.88   $178.90   $178.90  
  Purchase #4 $45.25   4.209%   $47.1546   $47.15   $47.15   $47.20  
  Purchase #5 $83.93   8.183%   $90.798   $90.80   $90.80   $90.80  
  Purchase #6 $196.32   3.150%   $202.5041   $202.50   $202.50   $202.50  
  Purchase #7 $11.93   11.387%   $13.2885   $13.29   $13.30   $13.30  
  7 purchase totals = $860.37       $937.1312   $937.12   $937.15   $937.20