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 $65.41   13.236%   $74.0677   $74.07   $74.05   $74.10  
  Purchase #2 $106.93   13.602%   $121.4746   $121.47   $121.45   $121.50  
  Purchase #3 $101.46   3.168%   $104.6743   $104.67   $104.65   $104.70  
  Purchase #4 $249.87   6.557%   $266.254   $266.25   $266.25   $266.30  
  Purchase #5 $192.87   12.385%   $216.7569   $216.76   $216.75   $216.80  
  Purchase #6 $204.36   7.856%   $220.4145   $220.41   $220.40   $220.40  
  Purchase #7 $146.76   7.839%   $158.2645   $158.26   $158.25   $158.30  
  7 purchase totals = $1,067.66       $1,161.9065   $1,161.89   $1,161.80   $1,162.10