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 $67.81   13.621%   $77.0464   $77.05   $77.05   $77.00  
  Purchase #2 $167.66   5.766%   $177.3273   $177.33   $177.35   $177.30  
  Purchase #3 $40.91   9.560%   $44.821   $44.82   $44.80   $44.80  
  Purchase #4 $90.50   8.511%   $98.2025   $98.20   $98.20   $98.20  
  Purchase #5 $103.70   10.461%   $114.5481   $114.55   $114.55   $114.50  
  Purchase #6 $248.46   8.706%   $270.0909   $270.09   $270.10   $270.10  
  Purchase #7 $119.35   13.586%   $135.5649   $135.56   $135.55   $135.60  
  7 purchase totals = $838.39       $917.6011   $917.60   $917.60   $917.50