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 $168.80   11.244%   $187.7799   $187.78   $187.80   $187.80  
  Purchase #2 $237.93   9.790%   $261.2233   $261.22   $261.20   $261.20  
  Purchase #3 $136.69   3.806%   $141.8924   $141.89   $141.90   $141.90  
  Purchase #4 $145.27   8.253%   $157.2591   $157.26   $157.25   $157.30  
  Purchase #5 $231.62   11.246%   $257.668   $257.67   $257.65   $257.70  
  Purchase #6 $182.37   13.655%   $207.2726   $207.27   $207.25   $207.30  
  Purchase #7 $180.28   12.498%   $202.8114   $202.81   $202.80   $202.80  
  7 purchase totals = $1,282.96       $1,415.9067   $1,415.90   $1,415.85   $1,416.00