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 $238.77   8.464%   $258.9795   $258.98   $259.00   $259.00  
  Purchase #2 $231.69   5.834%   $245.2068   $245.21   $245.20   $245.20  
  Purchase #3 $177.74   11.397%   $197.997   $198.00   $198.00   $198.00  
  Purchase #4 $223.54   8.678%   $242.9388   $242.94   $242.95   $242.90  
  Purchase #5 $164.66   4.179%   $171.5411   $171.54   $171.55   $171.50  
  Purchase #6 $82.43   12.251%   $92.5285   $92.53   $92.55   $92.50  
  Purchase #7 $48.32   5.381%   $50.9201   $50.92   $50.90   $50.90  
  7 purchase totals = $1,167.15       $1,260.1118   $1,260.12   $1,260.15   $1,260.00