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 $42.47   11.866%   $47.5095   $47.51   $47.50   $47.50  
  Purchase #2 $88.94   10.573%   $98.3436   $98.34   $98.35   $98.30  
  Purchase #3 $35.76   12.419%   $40.201   $40.20   $40.20   $40.20  
  Purchase #4 $151.91   3.681%   $157.5018   $157.50   $157.50   $157.50  
  Purchase #5 $5.90   9.195%   $6.4425   $6.44   $6.45   $6.40  
  Purchase #6 $235.51   5.469%   $248.39   $248.39   $248.40   $248.40  
  Purchase #7 $48.50   11.703%   $54.176   $54.18   $54.20   $54.20  
  7 purchase totals = $608.99       $652.5644   $652.56   $652.60   $652.50