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 $241.66   7.192%   $259.0402   $259.04   $259.05   $259.00  
  Purchase #2 $245.72   5.284%   $258.7038   $258.70   $258.70   $258.70  
  Purchase #3 $154.57   13.326%   $175.168   $175.17   $175.15   $175.20  
  Purchase #4 $42.32   12.463%   $47.5943   $47.59   $47.60   $47.60  
  Purchase #5 $246.79   11.791%   $275.889   $275.89   $275.90   $275.90  
  Purchase #6 $137.61   6.740%   $146.8849   $146.88   $146.90   $146.90  
  Purchase #7 $171.60   9.511%   $187.9209   $187.92   $187.90   $187.90  
  7 purchase totals = $1,240.27       $1,351.2011   $1,351.19   $1,351.20   $1,351.20