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 $233.26   8.710%   $253.5769   $253.58   $253.60   $253.60  
  Purchase #2 $208.77   3.243%   $215.5404   $215.54   $215.55   $215.50  
  Purchase #3 $236.92   8.128%   $256.1769   $256.18   $256.20   $256.20  
  Purchase #4 $69.82   10.851%   $77.3962   $77.40   $77.40   $77.40  
  Purchase #5 $26.42   11.470%   $29.4504   $29.45   $29.45   $29.50  
  Purchase #6 $114.42   8.183%   $123.783   $123.78   $123.80   $123.80  
  Purchase #7 $106.65   13.699%   $121.26   $121.26   $121.25   $121.30  
  7 purchase totals = $996.26       $1,077.1838   $1,077.19   $1,077.25   $1,077.30