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 $221.39   13.726%   $251.778   $251.78   $251.80   $251.80  
  Purchase #2 $236.92   10.482%   $261.754   $261.75   $261.75   $261.80  
  Purchase #3 $164.31   6.226%   $174.5399   $174.54   $174.55   $174.50  
  Purchase #4 $194.64   5.256%   $204.8703   $204.87   $204.85   $204.90  
  Purchase #5 $218.42   13.725%   $248.3981   $248.40   $248.40   $248.40  
  Purchase #6 $34.56   12.861%   $39.0048   $39.00   $39.00   $39.00  
  Purchase #7 $16.67   10.508%   $18.4217   $18.42   $18.40   $18.40  
  7 purchase totals = $1,086.91       $1,198.7668   $1,198.76   $1,198.75   $1,198.80