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 $144.76   3.637%   $150.0249   $150.02   $150.00   $150.00  
  Purchase #2 $234.73   13.353%   $266.0735   $266.07   $266.05   $266.10  
  Purchase #3 $237.75   6.242%   $252.5904   $252.59   $252.60   $252.60  
  Purchase #4 $186.36   8.689%   $202.5528   $202.55   $202.55   $202.60  
  Purchase #5 $69.46   6.263%   $73.8103   $73.81   $73.80   $73.80  
  Purchase #6 $17.48   6.166%   $18.5578   $18.56   $18.55   $18.60  
  Purchase #7 $95.77   13.509%   $108.7076   $108.71   $108.70   $108.70  
  7 purchase totals = $986.31       $1,072.3173   $1,072.31   $1,072.25   $1,072.40