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 $246.57   4.441%   $257.5202   $257.52   $257.50   $257.50  
  Purchase #2 $184.51   5.632%   $194.9016   $194.90   $194.90   $194.90  
  Purchase #3 $26.46   3.376%   $27.3533   $27.35   $27.35   $27.40  
  Purchase #4 $141.42   10.542%   $156.3285   $156.33   $156.35   $156.30  
  Purchase #5 $186.36   12.167%   $209.0344   $209.03   $209.05   $209.00  
  Purchase #6 $114.64   8.806%   $124.7352   $124.74   $124.75   $124.70  
  Purchase #7 $63.70   4.381%   $66.4907   $66.49   $66.50   $66.50  
  7 purchase totals = $963.66       $1,036.3639   $1,036.36   $1,036.40   $1,036.30