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 $44.29   6.616%   $47.2202   $47.22   $47.20   $47.20  
  Purchase #2 $222.95   8.717%   $242.3846   $242.38   $242.40   $242.40  
  Purchase #3 $13.56   6.694%   $14.4677   $14.47   $14.45   $14.50  
  Purchase #4 $249.93   4.697%   $261.6692   $261.67   $261.65   $261.70  
  Purchase #5 $176.31   4.123%   $183.5793   $183.58   $183.60   $183.60  
  Purchase #6 $211.53   4.547%   $221.1483   $221.15   $221.15   $221.10  
  Purchase #7 $12.86   12.322%   $14.4446   $14.44   $14.45   $14.40  
  7 purchase totals = $931.43       $984.9139   $984.91   $984.90   $984.90