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 $57.89   9.182%   $63.2055   $63.21   $63.20   $63.20  
  Purchase #2 $186.67   10.344%   $205.9791   $205.98   $206.00   $206.00  
  Purchase #3 $40.38   8.688%   $43.8882   $43.89   $43.90   $43.90  
  Purchase #4 $31.35   13.628%   $35.6224   $35.62   $35.60   $35.60  
  Purchase #5 $194.74   12.478%   $219.0397   $219.04   $219.05   $219.00  
  Purchase #6 $221.46   9.364%   $242.1975   $242.20   $242.20   $242.20  
  Purchase #7 $137.74   3.859%   $143.0554   $143.06   $143.05   $143.10  
  7 purchase totals = $870.23       $952.9878   $953.00   $953.00   $953.00