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 $226.50   13.548%   $257.1862   $257.19   $257.20   $257.20  
  Purchase #2 $172.44   8.871%   $187.7372   $187.74   $187.75   $187.70  
  Purchase #3 $249.63   7.105%   $267.3662   $267.37   $267.35   $267.40  
  Purchase #4 $32.58   10.280%   $35.9292   $35.93   $35.95   $35.90  
  Purchase #5 $162.94   10.474%   $180.0063   $180.01   $180.00   $180.00  
  Purchase #6 $78.87   8.635%   $85.6804   $85.68   $85.70   $85.70  
  Purchase #7 $40.75   11.252%   $45.3352   $45.34   $45.35   $45.30  
  7 purchase totals = $963.71       $1,059.2407   $1,059.26   $1,059.30   $1,059.20