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 $55.46   11.782%   $61.9943   $61.99   $62.00   $62.00  
  Purchase #2 $28.69   7.782%   $30.9227   $30.92   $30.90   $30.90  
  Purchase #3 $156.64   7.741%   $168.7655   $168.77   $168.75   $168.80  
  Purchase #4 $61.25   5.314%   $64.5048   $64.50   $64.50   $64.50  
  Purchase #5 $69.45   11.477%   $77.4208   $77.42   $77.40   $77.40  
  Purchase #6 $54.25   4.138%   $56.4949   $56.49   $56.50   $56.50  
  Purchase #7 $183.26   9.263%   $200.2354   $200.24   $200.25   $200.20  
  7 purchase totals = $609.00       $660.3384   $660.33   $660.30   $660.30