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 $56.74   8.317%   $61.4591   $61.46   $61.45   $61.50  
  Purchase #2 $168.44   3.159%   $173.761   $173.76   $173.75   $173.80  
  Purchase #3 $73.29   11.716%   $81.8767   $81.88   $81.90   $81.90  
  Purchase #4 $64.69   7.481%   $69.5295   $69.53   $69.55   $69.50  
  Purchase #5 $111.26   12.390%   $125.0451   $125.05   $125.05   $125.00  
  Purchase #6 $130.90   5.854%   $138.5629   $138.56   $138.55   $138.60  
  Purchase #7 $122.85   5.581%   $129.7063   $129.71   $129.70   $129.70  
  7 purchase totals = $728.17       $779.9406   $779.95   $779.95   $780.00