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 $41.49   4.841%   $43.4985   $43.50   $43.50   $43.50  
  Purchase #2 $31.41   7.195%   $33.6699   $33.67   $33.65   $33.70  
  Purchase #3 $191.67   5.596%   $202.3959   $202.40   $202.40   $202.40  
  Purchase #4 $242.29   8.874%   $263.7908   $263.79   $263.80   $263.80  
  Purchase #5 $87.70   6.105%   $93.0541   $93.05   $93.05   $93.10  
  Purchase #6 $17.94   7.242%   $19.2392   $19.24   $19.25   $19.20  
  Purchase #7 $214.82   5.867%   $227.4235   $227.42   $227.40   $227.40  
  7 purchase totals = $827.32       $883.0719   $883.07   $883.05   $883.10