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 $43.82   13.696%   $49.8216   $49.82   $49.80   $49.80  
  Purchase #2 $182.91   10.617%   $202.3296   $202.33   $202.35   $202.30  
  Purchase #3 $131.32   4.502%   $137.232   $137.23   $137.25   $137.20  
  Purchase #4 $77.46   3.651%   $80.2881   $80.29   $80.30   $80.30  
  Purchase #5 $66.57   13.725%   $75.7067   $75.71   $75.70   $75.70  
  Purchase #6 $35.58   5.506%   $37.539   $37.54   $37.55   $37.50  
  Purchase #7 $205.75   7.518%   $221.2183   $221.22   $221.20   $221.20  
  7 purchase totals = $743.41       $804.1353   $804.14   $804.15   $804.00