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 $63.72   8.338%   $69.033   $69.03   $69.05   $69.00  
  Purchase #2 $16.58   7.702%   $17.857   $17.86   $17.85   $17.90  
  Purchase #3 $234.56   11.562%   $261.6798   $261.68   $261.70   $261.70  
  Purchase #4 $56.70   13.279%   $64.2292   $64.23   $64.25   $64.20  
  Purchase #5 $31.43   10.765%   $34.8134   $34.81   $34.80   $34.80  
  Purchase #6 $126.96   12.208%   $142.4593   $142.46   $142.45   $142.50  
  Purchase #7 $188.87   3.659%   $195.7808   $195.78   $195.80   $195.80  
  7 purchase totals = $718.82       $785.8525   $785.85   $785.90   $785.90