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 $53.50   11.794%   $59.8098   $59.81   $59.80   $59.80  
  Purchase #2 $247.42   5.857%   $261.9114   $261.91   $261.90   $261.90  
  Purchase #3 $28.53   6.230%   $30.3074   $30.31   $30.30   $30.30  
  Purchase #4 $144.66   11.627%   $161.4796   $161.48   $161.50   $161.50  
  Purchase #5 $133.46   10.748%   $147.8043   $147.80   $147.80   $147.80  
  Purchase #6 $215.36   7.340%   $231.1674   $231.17   $231.15   $231.20  
  Purchase #7 $51.29   12.831%   $57.871   $57.87   $57.85   $57.90  
  7 purchase totals = $874.22       $950.3509   $950.35   $950.30   $950.40