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 $208.28   12.221%   $233.7339   $233.73   $233.75   $233.70  
  Purchase #2 $250.97   6.591%   $267.5114   $267.51   $267.50   $267.50  
  Purchase #3 $47.51   6.686%   $50.6865   $50.69   $50.70   $50.70  
  Purchase #4 $13.45   11.676%   $15.0204   $15.02   $15.00   $15.00  
  Purchase #5 $118.61   13.428%   $134.537   $134.54   $134.55   $134.50  
  Purchase #6 $13.60   7.232%   $14.5836   $14.58   $14.60   $14.60  
  Purchase #7 $156.74   11.121%   $174.1711   $174.17   $174.15   $174.20  
  7 purchase totals = $809.16       $890.2439   $890.24   $890.25   $890.20