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 $236.83   11.605%   $264.3141   $264.31   $264.30   $264.30  
  Purchase #2 $27.61   9.761%   $30.305   $30.31   $30.30   $30.30  
  Purchase #3 $129.69   7.163%   $138.9797   $138.98   $139.00   $139.00  
  Purchase #4 $29.55   3.866%   $30.6924   $30.69   $30.70   $30.70  
  Purchase #5 $159.81   8.605%   $173.5617   $173.56   $173.55   $173.60  
  Purchase #6 $162.30   11.841%   $181.5179   $181.52   $181.50   $181.50  
  Purchase #7 $228.77   10.151%   $251.9924   $251.99   $252.00   $252.00  
  7 purchase totals = $974.56       $1,071.3632   $1,071.36   $1,071.35   $1,071.40