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 $69.31   5.364%   $73.0278   $73.03   $73.05   $73.00  
  Purchase #2 $121.27   4.748%   $127.0279   $127.03   $127.05   $127.00  
  Purchase #3 $22.51   6.565%   $23.9878   $23.99   $24.00   $24.00  
  Purchase #4 $209.84   13.780%   $238.756   $238.76   $238.75   $238.80  
  Purchase #5 $183.61   12.752%   $207.0239   $207.02   $207.00   $207.00  
  Purchase #6 $222.74   12.388%   $250.333   $250.33   $250.35   $250.30  
  Purchase #7 $36.38   6.673%   $38.8076   $38.81   $38.80   $38.80  
  7 purchase totals = $865.66       $958.9640   $958.97   $959.00   $958.90