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 $76.32   13.684%   $86.7636   $86.76   $86.75   $86.80  
  Purchase #2 $228.59   12.125%   $256.3065   $256.31   $256.30   $256.30  
  Purchase #3 $19.74   10.642%   $21.8407   $21.84   $21.85   $21.80  
  Purchase #4 $94.71   3.610%   $98.129   $98.13   $98.15   $98.10  
  Purchase #5 $15.38   5.235%   $16.1851   $16.19   $16.20   $16.20  
  Purchase #6 $228.56   8.555%   $248.1133   $248.11   $248.10   $248.10  
  Purchase #7 $238.32   10.718%   $263.8631   $263.86   $263.85   $263.90  
  7 purchase totals = $901.62       $991.2013   $991.20   $991.20   $991.20