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 $56.83   11.147%   $63.1648   $63.16   $63.15   $63.20  
  Purchase #2 $204.97   5.289%   $215.8109   $215.81   $215.80   $215.80  
  Purchase #3 $11.32   5.542%   $11.9474   $11.95   $11.95   $11.90  
  Purchase #4 $240.63   4.586%   $251.6653   $251.67   $251.65   $251.70  
  Purchase #5 $183.95   8.297%   $199.2123   $199.21   $199.20   $199.20  
  Purchase #6 $140.63   4.172%   $146.4971   $146.50   $146.50   $146.50  
  Purchase #7 $13.73   5.698%   $14.5123   $14.51   $14.50   $14.50  
  7 purchase totals = $852.06       $902.8101   $902.81   $902.75   $902.80