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 $205.25   8.529%   $222.7558   $222.76   $222.75   $222.80  
  Purchase #2 $134.56   8.493%   $145.9882   $145.99   $146.00   $146.00  
  Purchase #3 $204.76   11.296%   $227.8897   $227.89   $227.90   $227.90  
  Purchase #4 $86.57   13.584%   $98.3297   $98.33   $98.35   $98.30  
  Purchase #5 $155.35   5.501%   $163.8958   $163.90   $163.90   $163.90  
  Purchase #6 $108.73   5.442%   $114.6471   $114.65   $114.65   $114.60  
  Purchase #7 $239.30   8.230%   $258.9944   $258.99   $259.00   $259.00  
  7 purchase totals = $1,134.52       $1,232.5007   $1,232.51   $1,232.55   $1,232.50