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 $24.87   7.612%   $26.7631   $26.76   $26.75   $26.80  
  Purchase #2 $61.53   10.416%   $67.939   $67.94   $67.95   $67.90  
  Purchase #3 $239.83   3.177%   $247.4494   $247.45   $247.45   $247.40  
  Purchase #4 $46.61   6.198%   $49.4989   $49.50   $49.50   $49.50  
  Purchase #5 $213.96   3.252%   $220.918   $220.92   $220.90   $220.90  
  Purchase #6 $236.43   4.866%   $247.9347   $247.93   $247.95   $247.90  
  Purchase #7 $213.53   4.454%   $223.0406   $223.04   $223.05   $223.00  
  7 purchase totals = $1,036.76       $1,083.5437   $1,083.54   $1,083.55   $1,083.40