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 $128.57   11.567%   $143.4417   $143.44   $143.45   $143.40  
  Purchase #2 $90.28   5.796%   $95.5126   $95.51   $95.50   $95.50  
  Purchase #3 $194.44   5.859%   $205.8322   $205.83   $205.85   $205.80  
  Purchase #4 $104.41   8.473%   $113.2567   $113.26   $113.25   $113.30  
  Purchase #5 $247.70   5.394%   $261.0609   $261.06   $261.05   $261.10  
  Purchase #6 $111.94   6.667%   $119.403   $119.40   $119.40   $119.40  
  Purchase #7 $92.63   4.811%   $97.0864   $97.09   $97.10   $97.10  
  7 purchase totals = $969.97       $1,035.5935   $1,035.59   $1,035.60   $1,035.60