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 $237.63   12.556%   $267.4668   $267.47   $267.45   $267.50  
  Purchase #2 $119.93   5.398%   $126.4038   $126.40   $126.40   $126.40  
  Purchase #3 $120.34   13.212%   $136.2393   $136.24   $136.25   $136.20  
  Purchase #4 $151.52   6.441%   $161.2794   $161.28   $161.30   $161.30  
  Purchase #5 $222.59   13.383%   $252.3792   $252.38   $252.40   $252.40  
  Purchase #6 $109.31   9.531%   $119.7283   $119.73   $119.75   $119.70  
  Purchase #7 $19.25   3.339%   $19.8928   $19.89   $19.90   $19.90  
  7 purchase totals = $980.57       $1,083.3896   $1,083.39   $1,083.45   $1,083.40