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 $62.90   5.107%   $66.1123   $66.11   $66.10   $66.10  
  Purchase #2 $24.75   6.439%   $26.3437   $26.34   $26.35   $26.30  
  Purchase #3 $8.82   8.691%   $9.5865   $9.59   $9.60   $9.60  
  Purchase #4 $248.35   13.455%   $281.7655   $281.77   $281.75   $281.80  
  Purchase #5 $182.92   7.368%   $196.3975   $196.40   $196.40   $196.40  
  Purchase #6 $100.56   8.329%   $108.9356   $108.94   $108.95   $108.90  
  Purchase #7 $232.39   12.736%   $261.9872   $261.99   $262.00   $262.00  
  7 purchase totals = $860.69       $951.1283   $951.14   $951.15   $951.10