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 $58.86   4.229%   $61.3492   $61.35   $61.35   $61.30  
  Purchase #2 $21.99   12.411%   $24.7192   $24.72   $24.70   $24.70  
  Purchase #3 $108.91   8.535%   $118.2055   $118.21   $118.20   $118.20  
  Purchase #4 $102.25   9.758%   $112.2276   $112.23   $112.25   $112.20  
  Purchase #5 $83.88   4.502%   $87.6563   $87.66   $87.65   $87.70  
  Purchase #6 $50.54   12.595%   $56.9055   $56.91   $56.90   $56.90  
  Purchase #7 $136.34   9.166%   $148.8369   $148.84   $148.85   $148.80  
  7 purchase totals = $562.77       $609.9002   $609.92   $609.90   $609.80