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 $250.80   6.494%   $267.087   $267.09   $267.10   $267.10  
  Purchase #2 $159.73   10.581%   $176.631   $176.63   $176.65   $176.60  
  Purchase #3 $96.90   3.441%   $100.2343   $100.23   $100.25   $100.20  
  Purchase #4 $11.49   3.314%   $11.8708   $11.87   $11.85   $11.90  
  Purchase #5 $53.66   5.406%   $56.5609   $56.56   $56.55   $56.60  
  Purchase #6 $52.49   3.197%   $54.1681   $54.17   $54.15   $54.20  
  Purchase #7 $113.91   6.348%   $121.141   $121.14   $121.15   $121.10  
  7 purchase totals = $738.98       $787.6931   $787.69   $787.70   $787.70