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 $78.82   9.436%   $86.2575   $86.26   $86.25   $86.30  
  Purchase #2 $31.88   8.216%   $34.4993   $34.50   $34.50   $34.50  
  Purchase #3 $175.69   6.397%   $186.9289   $186.93   $186.95   $186.90  
  Purchase #4 $207.51   11.345%   $231.052   $231.05   $231.05   $231.10  
  Purchase #5 $67.58   9.127%   $73.748   $73.75   $73.75   $73.70  
  Purchase #6 $250.42   8.538%   $271.8009   $271.80   $271.80   $271.80  
  Purchase #7 $66.67   8.487%   $72.3283   $72.33   $72.35   $72.30  
  7 purchase totals = $878.57       $956.6149   $956.62   $956.65   $956.60