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 $60.50   5.709%   $63.9539   $63.95   $63.95   $64.00  
  Purchase #2 $97.46   4.250%   $101.6021   $101.60   $101.60   $101.60  
  Purchase #3 $248.70   4.595%   $260.1278   $260.13   $260.15   $260.10  
  Purchase #4 $114.78   7.597%   $123.4998   $123.50   $123.50   $123.50  
  Purchase #5 $99.62   12.495%   $112.0675   $112.07   $112.05   $112.10  
  Purchase #6 $188.81   12.229%   $211.8996   $211.90   $211.90   $211.90  
  Purchase #7 $9.76   5.845%   $10.3305   $10.33   $10.35   $10.30  
  7 purchase totals = $819.63       $883.4812   $883.48   $883.50   $883.50