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 $241.53   8.646%   $262.4127   $262.41   $262.40   $262.40  
  Purchase #2 $17.26   4.782%   $18.0854   $18.09   $18.10   $18.10  
  Purchase #3 $70.98   3.193%   $73.2464   $73.25   $73.25   $73.20  
  Purchase #4 $92.97   11.740%   $103.8847   $103.88   $103.90   $103.90  
  Purchase #5 $165.73   7.330%   $177.878   $177.88   $177.90   $177.90  
  Purchase #6 $170.76   11.780%   $190.8755   $190.88   $190.90   $190.90  
  Purchase #7 $221.50   13.156%   $250.6405   $250.64   $250.65   $250.60  
  7 purchase totals = $980.73       $1,077.0232   $1,077.03   $1,077.10   $1,077.00