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 $42.92   13.848%   $48.8636   $48.86   $48.85   $48.90  
  Purchase #2 $29.81   4.179%   $31.0558   $31.06   $31.05   $31.10  
  Purchase #3 $141.74   11.536%   $158.0911   $158.09   $158.10   $158.10  
  Purchase #4 $219.50   7.693%   $236.3861   $236.39   $236.40   $236.40  
  Purchase #5 $216.63   10.550%   $239.4845   $239.48   $239.50   $239.50  
  Purchase #6 $126.27   8.295%   $136.7441   $136.74   $136.75   $136.70  
  Purchase #7 $99.67   8.396%   $108.0383   $108.04   $108.05   $108.00  
  7 purchase totals = $876.54       $958.6635   $958.66   $958.70   $958.70