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 $53.92   5.457%   $56.8624   $56.86   $56.85   $56.90  
  Purchase #2 $239.51   8.443%   $259.7318   $259.73   $259.75   $259.70  
  Purchase #3 $78.56   6.188%   $83.4213   $83.42   $83.40   $83.40  
  Purchase #4 $38.78   6.213%   $41.1894   $41.19   $41.20   $41.20  
  Purchase #5 $17.33   11.469%   $19.3176   $19.32   $19.30   $19.30  
  Purchase #6 $10.60   10.233%   $11.6847   $11.68   $11.70   $11.70  
  Purchase #7 $144.97   5.308%   $152.665   $152.67   $152.65   $152.70  
  7 purchase totals = $583.67       $624.8722   $624.87   $624.85   $624.90