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 $235.46   13.385%   $266.9763   $266.98   $267.00   $267.00  
  Purchase #2 $102.95   4.776%   $107.8669   $107.87   $107.85   $107.90  
  Purchase #3 $180.61   5.385%   $190.3358   $190.34   $190.35   $190.30  
  Purchase #4 $35.75   5.388%   $37.6762   $37.68   $37.70   $37.70  
  Purchase #5 $248.41   8.165%   $268.6927   $268.69   $268.70   $268.70  
  Purchase #6 $174.97   7.805%   $188.6264   $188.63   $188.65   $188.60  
  Purchase #7 $149.83   3.407%   $154.9347   $154.93   $154.95   $154.90  
  7 purchase totals = $1,127.98       $1,215.1090   $1,215.12   $1,215.20   $1,215.10