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 $232.95   13.747%   $264.9736   $264.97   $264.95   $265.00  
  Purchase #2 $45.92   10.517%   $50.7494   $50.75   $50.75   $50.70  
  Purchase #3 $30.70   10.554%   $33.9401   $33.94   $33.95   $33.90  
  Purchase #4 $225.97   12.277%   $253.7123   $253.71   $253.70   $253.70  
  Purchase #5 $143.88   13.116%   $162.7513   $162.75   $162.75   $162.80  
  Purchase #6 $127.54   4.231%   $132.9362   $132.94   $132.95   $132.90  
  Purchase #7 $94.38   11.455%   $105.1912   $105.19   $105.20   $105.20  
  7 purchase totals = $901.34       $1,004.2541   $1,004.25   $1,004.25   $1,004.20