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 $49.82   7.794%   $53.703   $53.70   $53.70   $53.70  
  Purchase #2 $164.85   13.438%   $187.0025   $187.00   $187.00   $187.00  
  Purchase #3 $26.60   6.660%   $28.3716   $28.37   $28.35   $28.40  
  Purchase #4 $215.36   6.589%   $229.5501   $229.55   $229.55   $229.60  
  Purchase #5 $58.58   10.611%   $64.7959   $64.80   $64.80   $64.80  
  Purchase #6 $77.60   7.404%   $83.3455   $83.35   $83.35   $83.30  
  Purchase #7 $65.81   7.830%   $70.9629   $70.96   $70.95   $71.00  
  7 purchase totals = $658.62       $717.7315   $717.73   $717.70   $717.80