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 $208.85   5.844%   $221.0552   $221.06   $221.05   $221.10  
  Purchase #2 $36.96   6.228%   $39.2619   $39.26   $39.25   $39.30  
  Purchase #3 $245.77   6.761%   $262.3865   $262.39   $262.40   $262.40  
  Purchase #4 $47.50   12.870%   $53.6133   $53.61   $53.60   $53.60  
  Purchase #5 $107.74   5.241%   $113.3867   $113.39   $113.40   $113.40  
  Purchase #6 $131.72   4.346%   $137.4446   $137.44   $137.45   $137.40  
  Purchase #7 $165.63   10.631%   $183.2381   $183.24   $183.25   $183.20  
  7 purchase totals = $944.17       $1,010.3863   $1,010.39   $1,010.40   $1,010.40