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 $242.48   8.462%   $262.9987   $263.00   $263.00   $263.00  
  Purchase #2 $78.26   13.247%   $88.6271   $88.63   $88.65   $88.60  
  Purchase #3 $125.26   13.824%   $142.5759   $142.58   $142.60   $142.60  
  Purchase #4 $40.74   12.246%   $45.729   $45.73   $45.75   $45.70  
  Purchase #5 $61.28   9.117%   $66.8669   $66.87   $66.85   $66.90  
  Purchase #6 $133.79   10.492%   $147.8272   $147.83   $147.85   $147.80  
  Purchase #7 $46.55   8.229%   $50.3806   $50.38   $50.40   $50.40  
  7 purchase totals = $728.36       $805.0054   $805.02   $805.10   $805.00