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 $207.83   10.186%   $228.9996   $229.00   $229.00   $229.00  
  Purchase #2 $120.57   8.806%   $131.1874   $131.19   $131.20   $131.20  
  Purchase #3 $41.51   9.458%   $45.436   $45.44   $45.45   $45.40  
  Purchase #4 $153.80   5.256%   $161.8837   $161.88   $161.90   $161.90  
  Purchase #5 $152.46   9.806%   $167.4102   $167.41   $167.40   $167.40  
  Purchase #6 $50.28   8.420%   $54.5136   $54.51   $54.50   $54.50  
  Purchase #7 $121.93   10.571%   $134.8192   $134.82   $134.80   $134.80  
  7 purchase totals = $848.38       $924.2497   $924.25   $924.25   $924.20