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 $138.46   5.516%   $146.0975   $146.10   $146.10   $146.10  
  Purchase #2 $176.64   9.170%   $192.8379   $192.84   $192.85   $192.80  
  Purchase #3 $246.86   4.535%   $258.0551   $258.06   $258.05   $258.10  
  Purchase #4 $68.59   11.697%   $76.613   $76.61   $76.60   $76.60  
  Purchase #5 $106.89   7.807%   $115.2349   $115.23   $115.25   $115.20  
  Purchase #6 $112.34   12.751%   $126.6645   $126.66   $126.65   $126.70  
  Purchase #7 $48.84   7.330%   $52.42   $52.42   $52.40   $52.40  
  7 purchase totals = $898.62       $967.9229   $967.92   $967.90   $967.90