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 $232.95   7.537%   $250.5074   $250.51   $250.50   $250.50  
  Purchase #2 $96.86   7.175%   $103.8097   $103.81   $103.80   $103.80  
  Purchase #3 $125.28   4.568%   $131.0028   $131.00   $131.00   $131.00  
  Purchase #4 $113.79   13.423%   $129.064   $129.06   $129.05   $129.10  
  Purchase #5 $183.25   9.713%   $201.0491   $201.05   $201.05   $201.00  
  Purchase #6 $161.68   5.797%   $171.0526   $171.05   $171.05   $171.10  
  Purchase #7 $48.93   11.533%   $54.5731   $54.57   $54.55   $54.60  
  7 purchase totals = $962.74       $1,041.0587   $1,041.05   $1,041.00   $1,041.10