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 $88.97   8.766%   $96.7691   $96.77   $96.75   $96.80  
  Purchase #2 $249.58   4.141%   $259.9151   $259.92   $259.90   $259.90  
  Purchase #3 $146.32   10.586%   $161.8094   $161.81   $161.80   $161.80  
  Purchase #4 $233.77   6.372%   $248.6658   $248.67   $248.65   $248.70  
  Purchase #5 $70.62   10.531%   $78.057   $78.06   $78.05   $78.10  
  Purchase #6 $89.48   5.850%   $94.7146   $94.71   $94.70   $94.70  
  Purchase #7 $52.49   8.210%   $56.7994   $56.80   $56.80   $56.80  
  7 purchase totals = $931.23       $996.7304   $996.74   $996.65   $996.80