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 $62.33   5.751%   $65.9146   $65.91   $65.90   $65.90  
  Purchase #2 $120.98   3.486%   $125.1974   $125.20   $125.20   $125.20  
  Purchase #3 $230.75   12.641%   $259.9191   $259.92   $259.90   $259.90  
  Purchase #4 $82.31   5.318%   $86.6872   $86.69   $86.70   $86.70  
  Purchase #5 $237.40   11.105%   $263.7633   $263.76   $263.75   $263.80  
  Purchase #6 $208.51   9.312%   $227.9265   $227.93   $227.95   $227.90  
  Purchase #7 $208.42   13.699%   $236.9715   $236.97   $236.95   $237.00  
  7 purchase totals = $1,150.70       $1,266.3796   $1,266.38   $1,266.35   $1,266.40