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 $182.95   11.448%   $203.8941   $203.89   $203.90   $203.90  
  Purchase #2 $241.74   10.677%   $267.5506   $267.55   $267.55   $267.60  
  Purchase #3 $228.87   9.359%   $250.2899   $250.29   $250.30   $250.30  
  Purchase #4 $114.47   4.502%   $119.6234   $119.62   $119.60   $119.60  
  Purchase #5 $51.37   4.246%   $53.5512   $53.55   $53.55   $53.60  
  Purchase #6 $11.58   12.241%   $12.9975   $13.00   $13.00   $13.00  
  Purchase #7 $174.45   3.590%   $180.7128   $180.71   $180.70   $180.70  
  7 purchase totals = $1,005.43       $1,088.6195   $1,088.61   $1,088.60   $1,088.70