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 $93.94   4.386%   $98.0602   $98.06   $98.05   $98.10  
  Purchase #2 $72.55   13.102%   $82.0555   $82.06   $82.05   $82.10  
  Purchase #3 $236.74   10.534%   $261.6782   $261.68   $261.70   $261.70  
  Purchase #4 $50.92   13.375%   $57.7306   $57.73   $57.75   $57.70  
  Purchase #5 $208.65   3.621%   $216.2052   $216.21   $216.20   $216.20  
  Purchase #6 $42.97   8.415%   $46.5859   $46.59   $46.60   $46.60  
  Purchase #7 $174.91   12.142%   $196.1476   $196.15   $196.15   $196.10  
  7 purchase totals = $880.68       $958.4632   $958.48   $958.50   $958.50