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 $92.95   12.769%   $104.8188   $104.82   $104.80   $104.80  
  Purchase #2 $177.98   7.471%   $191.2769   $191.28   $191.30   $191.30  
  Purchase #3 $240.82   8.670%   $261.6991   $261.70   $261.70   $261.70  
  Purchase #4 $124.26   9.570%   $136.1517   $136.15   $136.15   $136.20  
  Purchase #5 $164.30   12.714%   $185.1891   $185.19   $185.20   $185.20  
  Purchase #6 $195.90   11.826%   $219.0671   $219.07   $219.05   $219.10  
  Purchase #7 $15.40   6.340%   $16.3764   $16.38   $16.40   $16.40  
  7 purchase totals = $1,011.61       $1,114.5791   $1,114.59   $1,114.60   $1,114.70