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 $22.62   10.647%   $25.0284   $25.03   $25.05   $25.00  
  Purchase #2 $245.25   5.388%   $258.4641   $258.46   $258.45   $258.50  
  Purchase #3 $210.39   3.558%   $217.8757   $217.88   $217.90   $217.90  
  Purchase #4 $231.44   8.399%   $250.8786   $250.88   $250.90   $250.90  
  Purchase #5 $62.91   5.104%   $66.1209   $66.12   $66.10   $66.10  
  Purchase #6 $87.49   11.614%   $97.6511   $97.65   $97.65   $97.70  
  Purchase #7 $114.27   7.590%   $122.9431   $122.94   $122.95   $122.90  
  7 purchase totals = $974.37       $1,038.9619   $1,038.96   $1,039.00   $1,039.00