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 $91.27   12.777%   $102.9316   $102.93   $102.95   $102.90  
  Purchase #2 $227.61   13.287%   $257.8525   $257.85   $257.85   $257.90  
  Purchase #3 $245.95   6.241%   $261.2997   $261.30   $261.30   $261.30  
  Purchase #4 $33.78   5.270%   $35.5602   $35.56   $35.55   $35.60  
  Purchase #5 $103.96   13.370%   $117.8595   $117.86   $117.85   $117.90  
  Purchase #6 $232.39   12.676%   $261.8478   $261.85   $261.85   $261.80  
  Purchase #7 $34.44   8.322%   $37.3061   $37.31   $37.30   $37.30  
  7 purchase totals = $969.40       $1,074.6574   $1,074.66   $1,074.65   $1,074.70