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 $188.47   12.255%   $211.567   $211.57   $211.55   $211.60  
  Purchase #2 $118.41   10.374%   $130.6939   $130.69   $130.70   $130.70  
  Purchase #3 $201.46   6.503%   $214.5609   $214.56   $214.55   $214.60  
  Purchase #4 $59.68   4.259%   $62.2218   $62.22   $62.20   $62.20  
  Purchase #5 $51.92   12.534%   $58.4277   $58.43   $58.45   $58.40  
  Purchase #6 $231.70   12.709%   $261.1468   $261.15   $261.15   $261.10  
  Purchase #7 $208.94   7.646%   $224.9156   $224.92   $224.90   $224.90  
  7 purchase totals = $1,060.58       $1,163.5337   $1,163.54   $1,163.50   $1,163.50