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 $87.57   7.268%   $93.9346   $93.93   $93.95   $93.90  
  Purchase #2 $175.86   9.241%   $192.1112   $192.11   $192.10   $192.10  
  Purchase #3 $89.85   13.163%   $101.677   $101.68   $101.70   $101.70  
  Purchase #4 $153.40   5.527%   $161.8784   $161.88   $161.90   $161.90  
  Purchase #5 $123.68   8.392%   $134.0592   $134.06   $134.05   $134.10  
  Purchase #6 $160.83   9.856%   $176.6814   $176.68   $176.70   $176.70  
  Purchase #7 $7.50   3.540%   $7.7655   $7.77   $7.75   $7.80  
  7 purchase totals = $798.69       $868.1073   $868.11   $868.15   $868.20