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 $248.38   6.539%   $264.6216   $264.62   $264.60   $264.60  
  Purchase #2 $15.65   7.316%   $16.795   $16.80   $16.80   $16.80  
  Purchase #3 $54.38   10.565%   $60.1252   $60.13   $60.15   $60.10  
  Purchase #4 $118.36   10.475%   $130.7582   $130.76   $130.75   $130.80  
  Purchase #5 $202.35   5.839%   $214.1652   $214.17   $214.15   $214.20  
  Purchase #6 $111.96   6.848%   $119.627   $119.63   $119.65   $119.60  
  Purchase #7 $56.42   5.195%   $59.351   $59.35   $59.35   $59.40  
  7 purchase totals = $807.50       $865.4432   $865.46   $865.45   $865.50