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 $203.99   5.624%   $215.4624   $215.46   $215.45   $215.50  
  Purchase #2 $80.29   3.822%   $83.3587   $83.36   $83.35   $83.40  
  Purchase #3 $59.70   12.616%   $67.2318   $67.23   $67.25   $67.20  
  Purchase #4 $165.65   6.224%   $175.9601   $175.96   $175.95   $176.00  
  Purchase #5 $20.96   8.219%   $22.6827   $22.68   $22.70   $22.70  
  Purchase #6 $70.55   12.868%   $79.6284   $79.63   $79.65   $79.60  
  Purchase #7 $208.39   9.195%   $227.5515   $227.55   $227.55   $227.60  
  7 purchase totals = $809.53       $871.8756   $871.87   $871.90   $872.00