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 $223.83   10.494%   $247.3187   $247.32   $247.30   $247.30  
  Purchase #2 $225.26   8.557%   $244.5355   $244.54   $244.55   $244.50  
  Purchase #3 $81.36   13.274%   $92.1597   $92.16   $92.15   $92.20  
  Purchase #4 $26.49   13.527%   $30.0733   $30.07   $30.05   $30.10  
  Purchase #5 $10.66   9.280%   $11.6492   $11.65   $11.65   $11.60  
  Purchase #6 $90.36   13.731%   $102.7673   $102.77   $102.75   $102.80  
  Purchase #7 $235.64   7.235%   $252.6886   $252.69   $252.70   $252.70  
  7 purchase totals = $893.60       $981.1923   $981.20   $981.15   $981.20