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 $239.51   3.116%   $246.9731   $246.97   $246.95   $247.00  
  Purchase #2 $95.96   13.445%   $108.8618   $108.86   $108.85   $108.90  
  Purchase #3 $15.44   12.574%   $17.3814   $17.38   $17.40   $17.40  
  Purchase #4 $231.59   13.493%   $262.8384   $262.84   $262.85   $262.80  
  Purchase #5 $161.40   11.433%   $179.8529   $179.85   $179.85   $179.90  
  Purchase #6 $195.73   8.217%   $211.8131   $211.81   $211.80   $211.80  
  Purchase #7 $88.57   10.859%   $98.1878   $98.19   $98.20   $98.20  
  7 purchase totals = $1,028.20       $1,125.9085   $1,125.90   $1,125.90   $1,126.00