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 $50.39   12.541%   $56.7094   $56.71   $56.70   $56.70  
  Purchase #2 $201.71   6.521%   $214.8635   $214.86   $214.85   $214.90  
  Purchase #3 $10.50   8.697%   $11.4132   $11.41   $11.40   $11.40  
  Purchase #4 $30.61   5.214%   $32.206   $32.21   $32.20   $32.20  
  Purchase #5 $32.32   10.558%   $35.7323   $35.73   $35.75   $35.70  
  Purchase #6 $52.86   8.212%   $57.2009   $57.20   $57.20   $57.20  
  Purchase #7 $71.85   5.653%   $75.9117   $75.91   $75.90   $75.90  
  7 purchase totals = $450.24       $484.0370   $484.03   $484.00   $484.00