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 $23.81   9.190%   $25.9981   $26.00   $26.00   $26.00  
  Purchase #2 $63.29   3.260%   $65.3533   $65.35   $65.35   $65.40  
  Purchase #3 $117.46   5.728%   $124.1881   $124.19   $124.20   $124.20  
  Purchase #4 $61.27   10.377%   $67.628   $67.63   $67.65   $67.60  
  Purchase #5 $130.36   8.687%   $141.6844   $141.68   $141.70   $141.70  
  Purchase #6 $51.27   12.762%   $57.8131   $57.81   $57.80   $57.80  
  Purchase #7 $198.81   13.164%   $224.9813   $224.98   $225.00   $225.00  
  7 purchase totals = $646.27       $707.6463   $707.64   $707.70   $707.70