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 $51.37   13.763%   $58.4401   $58.44   $58.45   $58.40  
  Purchase #2 $139.89   13.685%   $159.0339   $159.03   $159.05   $159.00  
  Purchase #3 $60.35   6.597%   $64.3313   $64.33   $64.35   $64.30  
  Purchase #4 $121.99   6.611%   $130.0548   $130.05   $130.05   $130.10  
  Purchase #5 $245.50   8.102%   $265.3904   $265.39   $265.40   $265.40  
  Purchase #6 $82.89   13.240%   $93.8646   $93.86   $93.85   $93.90  
  Purchase #7 $244.29   11.856%   $273.253   $273.25   $273.25   $273.30  
  7 purchase totals = $946.28       $1,044.3681   $1,044.35   $1,044.40   $1,044.40