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 $240.27   8.190%   $259.9481   $259.95   $259.95   $259.90  
  Purchase #2 $104.94   8.167%   $113.5104   $113.51   $113.50   $113.50  
  Purchase #3 $32.48   8.790%   $35.335   $35.34   $35.35   $35.30  
  Purchase #4 $227.27   10.525%   $251.1902   $251.19   $251.20   $251.20  
  Purchase #5 $84.73   11.653%   $94.6036   $94.60   $94.60   $94.60  
  Purchase #6 $138.54   11.198%   $154.0537   $154.05   $154.05   $154.10  
  Purchase #7 $28.27   4.469%   $29.5334   $29.53   $29.55   $29.50  
  7 purchase totals = $856.50       $938.1744   $938.17   $938.20   $938.10