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 $209.93   8.294%   $227.3416   $227.34   $227.35   $227.30  
  Purchase #2 $73.71   13.645%   $83.7677   $83.77   $83.75   $83.80  
  Purchase #3 $61.32   13.618%   $69.6706   $69.67   $69.65   $69.70  
  Purchase #4 $111.63   13.242%   $126.412   $126.41   $126.40   $126.40  
  Purchase #5 $67.57   4.565%   $70.6546   $70.65   $70.65   $70.70  
  Purchase #6 $180.31   7.172%   $193.2418   $193.24   $193.25   $193.20  
  Purchase #7 $89.32   5.124%   $93.8968   $93.90   $93.90   $93.90  
  7 purchase totals = $793.79       $864.9851   $864.98   $864.95   $865.00