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 $50.95   11.676%   $56.8989   $56.90   $56.90   $56.90  
  Purchase #2 $110.81   11.351%   $123.388   $123.39   $123.40   $123.40  
  Purchase #3 $101.61   10.391%   $112.1683   $112.17   $112.15   $112.20  
  Purchase #4 $101.56   3.647%   $105.2639   $105.26   $105.25   $105.30  
  Purchase #5 $26.92   12.811%   $30.3687   $30.37   $30.35   $30.40  
  Purchase #6 $170.68   13.477%   $193.6825   $193.68   $193.70   $193.70  
  Purchase #7 $126.36   6.672%   $134.7907   $134.79   $134.80   $134.80  
  7 purchase totals = $688.89       $756.5610   $756.56   $756.55   $756.70