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 $245.28   12.544%   $276.0479   $276.05   $276.05   $276.00  
  Purchase #2 $193.98   5.271%   $204.2047   $204.20   $204.20   $204.20  
  Purchase #3 $231.69   12.709%   $261.1355   $261.14   $261.15   $261.10  
  Purchase #4 $55.75   7.495%   $59.9285   $59.93   $59.95   $59.90  
  Purchase #5 $46.71   3.400%   $48.2981   $48.30   $48.30   $48.30  
  Purchase #6 $5.54   3.287%   $5.7221   $5.72   $5.70   $5.70  
  Purchase #7 $141.73   10.603%   $156.7576   $156.76   $156.75   $156.80  
  7 purchase totals = $920.68       $1,012.0944   $1,012.10   $1,012.10   $1,012.00