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 $112.74   10.218%   $124.2598   $124.26   $124.25   $124.30  
  Purchase #2 $119.93   12.314%   $134.6982   $134.70   $134.70   $134.70  
  Purchase #3 $6.80   12.413%   $7.6441   $7.64   $7.65   $7.60  
  Purchase #4 $57.81   6.703%   $61.685   $61.69   $61.70   $61.70  
  Purchase #5 $20.95   4.243%   $21.8389   $21.84   $21.85   $21.80  
  Purchase #6 $57.71   7.237%   $61.8865   $61.89   $61.90   $61.90  
  Purchase #7 $236.84   4.160%   $246.6925   $246.69   $246.70   $246.70  
  7 purchase totals = $612.78       $658.7050   $658.71   $658.75   $658.70