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 $243.33   7.264%   $261.0055   $261.01   $261.00   $261.00  
  Purchase #2 $179.46   9.207%   $195.9829   $195.98   $196.00   $196.00  
  Purchase #3 $75.86   10.388%   $83.7403   $83.74   $83.75   $83.70  
  Purchase #4 $113.50   7.508%   $122.0216   $122.02   $122.00   $122.00  
  Purchase #5 $169.92   3.213%   $175.3795   $175.38   $175.40   $175.40  
  Purchase #6 $249.87   4.271%   $260.5419   $260.54   $260.55   $260.50  
  Purchase #7 $147.54   4.247%   $153.806   $153.81   $153.80   $153.80  
  7 purchase totals = $1,179.48       $1,252.4777   $1,252.48   $1,252.50   $1,252.40