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 $231.89   11.705%   $259.0327   $259.03   $259.05   $259.00  
  Purchase #2 $48.68   10.136%   $53.6142   $53.61   $53.60   $53.60  
  Purchase #3 $23.40   9.321%   $25.5811   $25.58   $25.60   $25.60  
  Purchase #4 $232.74   12.163%   $261.0482   $261.05   $261.05   $261.00  
  Purchase #5 $241.86   7.194%   $259.2594   $259.26   $259.25   $259.30  
  Purchase #6 $166.30   3.203%   $171.6266   $171.63   $171.65   $171.60  
  Purchase #7 $109.66   9.423%   $119.9933   $119.99   $120.00   $120.00  
  7 purchase totals = $1,054.53       $1,150.1555   $1,150.15   $1,150.20   $1,150.10