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 $79.57   8.136%   $86.0438   $86.04   $86.05   $86.00  
  Purchase #2 $213.38   4.216%   $222.3761   $222.38   $222.40   $222.40  
  Purchase #3 $157.91   5.164%   $166.0645   $166.06   $166.05   $166.10  
  Purchase #4 $69.85   6.229%   $74.201   $74.20   $74.20   $74.20  
  Purchase #5 $228.92   8.194%   $247.6777   $247.68   $247.70   $247.70  
  Purchase #6 $248.78   5.768%   $263.1296   $263.13   $263.15   $263.10  
  Purchase #7 $249.71   6.811%   $266.7177   $266.72   $266.70   $266.70  
  7 purchase totals = $1,248.12       $1,326.2104   $1,326.21   $1,326.25   $1,326.20