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 $63.48   10.683%   $70.2616   $70.26   $70.25   $70.30  
  Purchase #2 $73.49   4.666%   $76.919   $76.92   $76.90   $76.90  
  Purchase #3 $50.38   7.500%   $54.1585   $54.16   $54.15   $54.20  
  Purchase #4 $136.95   3.366%   $141.5597   $141.56   $141.55   $141.60  
  Purchase #5 $142.86   4.693%   $149.5644   $149.56   $149.55   $149.60  
  Purchase #6 $227.81   5.732%   $240.8681   $240.87   $240.85   $240.90  
  Purchase #7 $28.85   6.766%   $30.802   $30.80   $30.80   $30.80  
  7 purchase totals = $723.82       $764.1333   $764.13   $764.05   $764.30