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 $96.71   8.374%   $104.8085   $104.81   $104.80   $104.80  
  Purchase #2 $39.78   13.280%   $45.0628   $45.06   $45.05   $45.10  
  Purchase #3 $165.75   3.405%   $171.3938   $171.39   $171.40   $171.40  
  Purchase #4 $76.27   5.850%   $80.7318   $80.73   $80.75   $80.70  
  Purchase #5 $59.27   9.129%   $64.6808   $64.68   $64.70   $64.70  
  Purchase #6 $69.25   12.462%   $77.8799   $77.88   $77.90   $77.90  
  Purchase #7 $208.73   3.194%   $215.3968   $215.40   $215.40   $215.40  
  7 purchase totals = $715.76       $759.9544   $759.95   $760.00   $760.00