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 $60.91   13.341%   $69.036   $69.04   $69.05   $69.00  
  Purchase #2 $26.42   6.565%   $28.1545   $28.15   $28.15   $28.20  
  Purchase #3 $186.71   6.307%   $198.4858   $198.49   $198.50   $198.50  
  Purchase #4 $99.68   10.417%   $110.0637   $110.06   $110.05   $110.10  
  Purchase #5 $148.54   11.506%   $165.631   $165.63   $165.65   $165.60  
  Purchase #6 $181.57   8.339%   $196.7111   $196.71   $196.70   $196.70  
  Purchase #7 $210.73   12.821%   $237.7477   $237.75   $237.75   $237.70  
  7 purchase totals = $914.56       $1,005.8298   $1,005.83   $1,005.85   $1,005.80