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 $26.46   12.798%   $29.8464   $29.85   $29.85   $29.80  
  Purchase #2 $141.39   11.209%   $157.2384   $157.24   $157.25   $157.20  
  Purchase #3 $73.64   10.770%   $81.571   $81.57   $81.55   $81.60  
  Purchase #4 $106.82   13.356%   $121.0869   $121.09   $121.10   $121.10  
  Purchase #5 $47.50   11.582%   $53.0015   $53.00   $53.00   $53.00  
  Purchase #6 $205.33   9.503%   $224.8425   $224.84   $224.85   $224.80  
  Purchase #7 $114.72   3.630%   $118.8843   $118.88   $118.90   $118.90  
  7 purchase totals = $715.86       $786.4710   $786.47   $786.50   $786.40