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 $139.61   10.726%   $154.5846   $154.58   $154.60   $154.60  
  Purchase #2 $213.80   8.849%   $232.7192   $232.72   $232.70   $232.70  
  Purchase #3 $49.30   12.783%   $55.602   $55.60   $55.60   $55.60  
  Purchase #4 $18.88   6.737%   $20.1519   $20.15   $20.15   $20.20  
  Purchase #5 $58.87   13.318%   $66.7103   $66.71   $66.70   $66.70  
  Purchase #6 $173.67   3.520%   $179.7832   $179.78   $179.80   $179.80  
  Purchase #7 $174.75   9.873%   $192.0031   $192.00   $192.00   $192.00  
  7 purchase totals = $828.88       $901.5543   $901.54   $901.55   $901.60