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 $230.90   13.131%   $261.2195   $261.22   $261.20   $261.20  
  Purchase #2 $43.95   4.819%   $46.068   $46.07   $46.05   $46.10  
  Purchase #3 $142.36   9.194%   $155.4486   $155.45   $155.45   $155.40  
  Purchase #4 $61.41   13.176%   $69.5014   $69.50   $69.50   $69.50  
  Purchase #5 $86.97   5.231%   $91.5194   $91.52   $91.50   $91.50  
  Purchase #6 $200.75   7.287%   $215.3787   $215.38   $215.40   $215.40  
  Purchase #7 $116.97   4.743%   $122.5179   $122.52   $122.50   $122.50  
  7 purchase totals = $883.31       $961.6535   $961.66   $961.60   $961.60