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 $82.91   5.246%   $87.2595   $87.26   $87.25   $87.30  
  Purchase #2 $90.35   3.853%   $93.8312   $93.83   $93.85   $93.80  
  Purchase #3 $66.33   4.783%   $69.5026   $69.50   $69.50   $69.50  
  Purchase #4 $64.81   5.489%   $68.3674   $68.37   $68.35   $68.40  
  Purchase #5 $239.82   7.640%   $258.1422   $258.14   $258.15   $258.10  
  Purchase #6 $248.46   6.437%   $264.4534   $264.45   $264.45   $264.50  
  Purchase #7 $249.98   5.293%   $263.2114   $263.21   $263.20   $263.20  
  7 purchase totals = $1,042.66       $1,104.7677   $1,104.76   $1,104.75   $1,104.80