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 $242.90   8.467%   $263.4663   $263.47   $263.45   $263.50  
  Purchase #2 $188.86   7.815%   $203.6194   $203.62   $203.60   $203.60  
  Purchase #3 $52.27   6.867%   $55.8594   $55.86   $55.85   $55.90  
  Purchase #4 $158.79   11.304%   $176.7396   $176.74   $176.75   $176.70  
  Purchase #5 $89.25   3.375%   $92.2622   $92.26   $92.25   $92.30  
  Purchase #6 $53.39   6.316%   $56.7621   $56.76   $56.75   $56.80  
  Purchase #7 $197.82   10.450%   $218.4922   $218.49   $218.50   $218.50  
  7 purchase totals = $983.28       $1,067.2012   $1,067.20   $1,067.15   $1,067.30