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 $234.60   13.682%   $266.698   $266.70   $266.70   $266.70  
  Purchase #2 $70.85   5.166%   $74.5101   $74.51   $74.50   $74.50  
  Purchase #3 $71.66   7.106%   $76.7522   $76.75   $76.75   $76.80  
  Purchase #4 $105.51   7.363%   $113.2787   $113.28   $113.30   $113.30  
  Purchase #5 $201.42   12.231%   $226.0557   $226.06   $226.05   $226.10  
  Purchase #6 $182.78   10.299%   $201.6045   $201.60   $201.60   $201.60  
  Purchase #7 $83.54   9.105%   $91.1463   $91.15   $91.15   $91.10  
  7 purchase totals = $950.36       $1,050.0455   $1,050.05   $1,050.05   $1,050.10