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 $162.58   8.243%   $175.9815   $175.98   $176.00   $176.00  
  Purchase #2 $110.29   11.378%   $122.8388   $122.84   $122.85   $122.80  
  Purchase #3 $210.73   6.678%   $224.8025   $224.80   $224.80   $224.80  
  Purchase #4 $11.73   6.863%   $12.535   $12.54   $12.55   $12.50  
  Purchase #5 $82.97   9.484%   $90.8389   $90.84   $90.85   $90.80  
  Purchase #6 $193.88   10.736%   $214.695   $214.70   $214.70   $214.70  
  Purchase #7 $70.77   10.762%   $78.3863   $78.39   $78.40   $78.40  
  7 purchase totals = $842.95       $920.0780   $920.09   $920.15   $920.00