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 $196.92   3.551%   $203.9126   $203.91   $203.90   $203.90  
  Purchase #2 $46.66   11.193%   $51.8827   $51.88   $51.90   $51.90  
  Purchase #3 $34.29   13.177%   $38.8084   $38.81   $38.80   $38.80  
  Purchase #4 $180.68   10.110%   $198.9467   $198.95   $198.95   $198.90  
  Purchase #5 $226.53   11.806%   $253.2741   $253.27   $253.25   $253.30  
  Purchase #6 $82.29   5.593%   $86.8925   $86.89   $86.90   $86.90  
  Purchase #7 $17.32   5.794%   $18.3235   $18.32   $18.30   $18.30  
  7 purchase totals = $784.69       $852.0405   $852.03   $852.00   $852.00