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 $58.54   13.426%   $66.3996   $66.40   $66.40   $66.40  
  Purchase #2 $222.41   12.650%   $250.5449   $250.54   $250.55   $250.50  
  Purchase #3 $44.45   7.471%   $47.7709   $47.77   $47.75   $47.80  
  Purchase #4 $28.73   8.439%   $31.1545   $31.15   $31.15   $31.20  
  Purchase #5 $242.95   7.868%   $262.0653   $262.07   $262.05   $262.10  
  Purchase #6 $23.97   9.752%   $26.3076   $26.31   $26.30   $26.30  
  Purchase #7 $72.95   8.505%   $79.1544   $79.15   $79.15   $79.20  
  7 purchase totals = $694.00       $763.3972   $763.39   $763.35   $763.50