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 $84.99   10.683%   $94.0695   $94.07   $94.05   $94.10  
  Purchase #2 $245.75   6.274%   $261.1684   $261.17   $261.15   $261.20  
  Purchase #3 $178.41   5.557%   $188.3242   $188.32   $188.30   $188.30  
  Purchase #4 $62.48   13.332%   $70.8098   $70.81   $70.80   $70.80  
  Purchase #5 $174.95   12.700%   $197.1687   $197.17   $197.15   $197.20  
  Purchase #6 $176.90   5.820%   $187.1956   $187.20   $187.20   $187.20  
  Purchase #7 $244.82   5.480%   $258.2361   $258.24   $258.25   $258.20  
  7 purchase totals = $1,168.30       $1,256.9723   $1,256.98   $1,256.90   $1,257.00