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 $58.58   5.563%   $61.8388   $61.84   $61.85   $61.80  
  Purchase #2 $10.87   7.295%   $11.663   $11.66   $11.65   $11.70  
  Purchase #3 $102.65   9.595%   $112.4993   $112.50   $112.50   $112.50  
  Purchase #4 $77.78   6.535%   $82.8629   $82.86   $82.85   $82.90  
  Purchase #5 $67.39   9.412%   $73.7327   $73.73   $73.75   $73.70  
  Purchase #6 $168.99   4.120%   $175.9524   $175.95   $175.95   $176.00  
  Purchase #7 $28.44   12.602%   $32.024   $32.02   $32.00   $32.00  
  7 purchase totals = $514.70       $550.5731   $550.56   $550.55   $550.60