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 $66.64   8.617%   $72.3824   $72.38   $72.40   $72.40  
  Purchase #2 $228.71   7.243%   $245.2755   $245.28   $245.30   $245.30  
  Purchase #3 $132.96   7.592%   $143.0543   $143.05   $143.05   $143.10  
  Purchase #4 $76.38   8.798%   $83.0999   $83.10   $83.10   $83.10  
  Purchase #5 $154.38   12.143%   $173.1264   $173.13   $173.15   $173.10  
  Purchase #6 $237.97   6.287%   $252.9312   $252.93   $252.95   $252.90  
  Purchase #7 $219.78   6.426%   $233.9031   $233.90   $233.90   $233.90  
  7 purchase totals = $1,116.82       $1,203.7728   $1,203.77   $1,203.85   $1,203.80