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 $60.87   5.439%   $64.1807   $64.18   $64.20   $64.20  
  Purchase #2 $80.76   7.351%   $86.6967   $86.70   $86.70   $86.70  
  Purchase #3 $5.99   5.212%   $6.3022   $6.30   $6.30   $6.30  
  Purchase #4 $228.58   12.641%   $257.4748   $257.47   $257.45   $257.50  
  Purchase #5 $209.72   13.815%   $238.6928   $238.69   $238.70   $238.70  
  Purchase #6 $245.49   9.872%   $269.7248   $269.72   $269.70   $269.70  
  Purchase #7 $86.36   5.812%   $91.3792   $91.38   $91.40   $91.40  
  7 purchase totals = $917.77       $1,014.4512   $1,014.44   $1,014.45   $1,014.50