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 $77.39   11.176%   $86.0391   $86.04   $86.05   $86.00  
  Purchase #2 $96.42   9.457%   $105.5384   $105.54   $105.55   $105.50  
  Purchase #3 $248.82   11.587%   $277.6508   $277.65   $277.65   $277.70  
  Purchase #4 $35.92   6.503%   $38.2559   $38.26   $38.25   $38.30  
  Purchase #5 $14.71   3.747%   $15.2612   $15.26   $15.25   $15.30  
  Purchase #6 $240.33   7.808%   $259.095   $259.10   $259.10   $259.10  
  Purchase #7 $93.84   8.579%   $101.8905   $101.89   $101.90   $101.90  
  7 purchase totals = $807.43       $883.7309   $883.74   $883.75   $883.80