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 $231.27   6.189%   $245.5833   $245.58   $245.60   $245.60  
  Purchase #2 $159.95   5.163%   $168.2082   $168.21   $168.20   $168.20  
  Purchase #3 $132.40   8.373%   $143.4859   $143.49   $143.50   $143.50  
  Purchase #4 $82.95   13.126%   $93.838   $93.84   $93.85   $93.80  
  Purchase #5 $239.49   6.501%   $255.0592   $255.06   $255.05   $255.10  
  Purchase #6 $14.38   5.850%   $15.2212   $15.22   $15.20   $15.20  
  Purchase #7 $168.25   7.382%   $180.6702   $180.67   $180.65   $180.70  
  7 purchase totals = $1,028.69       $1,102.0660   $1,102.07   $1,102.05   $1,102.10