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 $123.29   8.843%   $134.1925   $134.19   $134.20   $134.20  
  Purchase #2 $152.81   13.566%   $173.5402   $173.54   $173.55   $173.50  
  Purchase #3 $120.35   6.289%   $127.9188   $127.92   $127.90   $127.90  
  Purchase #4 $69.89   5.426%   $73.6822   $73.68   $73.70   $73.70  
  Purchase #5 $238.26   9.600%   $261.133   $261.13   $261.15   $261.10  
  Purchase #6 $125.50   10.483%   $138.6562   $138.66   $138.65   $138.70  
  Purchase #7 $163.63   7.611%   $176.0839   $176.08   $176.10   $176.10  
  7 purchase totals = $993.73       $1,085.2068   $1,085.20   $1,085.25   $1,085.20