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 $248.39   13.228%   $281.247   $281.25   $281.25   $281.20  
  Purchase #2 $38.34   12.343%   $43.0723   $43.07   $43.05   $43.10  
  Purchase #3 $146.33   12.706%   $164.9227   $164.92   $164.90   $164.90  
  Purchase #4 $37.66   6.224%   $40.004   $40.00   $40.00   $40.00  
  Purchase #5 $186.63   11.156%   $207.4504   $207.45   $207.45   $207.50  
  Purchase #6 $54.82   11.524%   $61.1375   $61.14   $61.15   $61.10  
  Purchase #7 $205.75   4.392%   $214.7865   $214.79   $214.80   $214.80  
  7 purchase totals = $917.92       $1,012.6204   $1,012.62   $1,012.60   $1,012.60