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 $57.55   11.218%   $64.006   $64.01   $64.00   $64.00  
  Purchase #2 $84.45   9.421%   $92.406   $92.41   $92.40   $92.40  
  Purchase #3 $115.31   10.348%   $127.2423   $127.24   $127.25   $127.20  
  Purchase #4 $196.84   5.116%   $206.9103   $206.91   $206.90   $206.90  
  Purchase #5 $141.81   13.565%   $161.0465   $161.05   $161.05   $161.00  
  Purchase #6 $18.25   5.782%   $19.3052   $19.31   $19.30   $19.30  
  Purchase #7 $180.47   3.618%   $186.9994   $187.00   $187.00   $187.00  
  7 purchase totals = $794.68       $857.9157   $857.93   $857.90   $857.80