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 $48.27   11.238%   $53.6946   $53.69   $53.70   $53.70  
  Purchase #2 $50.59   10.333%   $55.8175   $55.82   $55.80   $55.80  
  Purchase #3 $218.38   12.307%   $245.256   $245.26   $245.25   $245.30  
  Purchase #4 $49.44   6.447%   $52.6274   $52.63   $52.65   $52.60  
  Purchase #5 $180.67   9.651%   $198.1065   $198.11   $198.10   $198.10  
  Purchase #6 $95.60   13.470%   $108.4773   $108.48   $108.50   $108.50  
  Purchase #7 $9.58   10.711%   $10.6061   $10.61   $10.60   $10.60  
  7 purchase totals = $652.53       $724.5854   $724.60   $724.60   $724.60