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 $62.79   5.650%   $66.3376   $66.34   $66.35   $66.30  
  Purchase #2 $187.68   9.777%   $206.0295   $206.03   $206.05   $206.00  
  Purchase #3 $216.65   8.796%   $235.7065   $235.71   $235.70   $235.70  
  Purchase #4 $129.26   6.408%   $137.543   $137.54   $137.55   $137.50  
  Purchase #5 $121.90   9.829%   $133.8816   $133.88   $133.90   $133.90  
  Purchase #6 $12.27   6.706%   $13.0928   $13.09   $13.10   $13.10  
  Purchase #7 $170.79   5.615%   $180.3799   $180.38   $180.40   $180.40  
  7 purchase totals = $901.34       $972.9709   $972.97   $973.05   $972.90