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 $234.56   11.347%   $261.1755   $261.18   $261.20   $261.20  
  Purchase #2 $107.86   8.749%   $117.2967   $117.30   $117.30   $117.30  
  Purchase #3 $138.59   3.687%   $143.6998   $143.70   $143.70   $143.70  
  Purchase #4 $202.50   4.378%   $211.3655   $211.37   $211.35   $211.40  
  Purchase #5 $22.97   6.536%   $24.4713   $24.47   $24.45   $24.50  
  Purchase #6 $105.74   12.423%   $118.8761   $118.88   $118.90   $118.90  
  Purchase #7 $80.92   3.345%   $83.6268   $83.63   $83.65   $83.60  
  7 purchase totals = $893.14       $960.5117   $960.53   $960.55   $960.60