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 $62.87   7.661%   $67.6865   $67.69   $67.70   $67.70  
  Purchase #2 $63.66   4.144%   $66.2981   $66.30   $66.30   $66.30  
  Purchase #3 $220.60   7.355%   $236.8251   $236.83   $236.85   $236.80  
  Purchase #4 $242.42   7.733%   $261.1663   $261.17   $261.15   $261.20  
  Purchase #5 $5.86   8.823%   $6.377   $6.38   $6.40   $6.40  
  Purchase #6 $59.53   10.136%   $65.564   $65.56   $65.55   $65.60  
  Purchase #7 $57.35   6.331%   $60.9808   $60.98   $61.00   $61.00  
  7 purchase totals = $712.29       $764.8978   $764.91   $764.95   $765.00