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 $186.63   11.748%   $208.5553   $208.56   $208.55   $208.60  
  Purchase #2 $170.75   13.597%   $193.9669   $193.97   $193.95   $194.00  
  Purchase #3 $108.39   4.807%   $113.6003   $113.60   $113.60   $113.60  
  Purchase #4 $228.32   7.709%   $245.9212   $245.92   $245.90   $245.90  
  Purchase #5 $112.70   8.856%   $122.6807   $122.68   $122.70   $122.70  
  Purchase #6 $184.29   10.636%   $203.8911   $203.89   $203.90   $203.90  
  Purchase #7 $72.33   12.776%   $81.5709   $81.57   $81.55   $81.60  
  7 purchase totals = $1,063.41       $1,170.1864   $1,170.19   $1,170.15   $1,170.30