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 $226.65   13.728%   $257.7645   $257.76   $257.75   $257.80  
  Purchase #2 $119.93   8.395%   $129.9981   $130.00   $130.00   $130.00  
  Purchase #3 $228.82   8.477%   $248.2171   $248.22   $248.20   $248.20  
  Purchase #4 $73.83   3.588%   $76.479   $76.48   $76.50   $76.50  
  Purchase #5 $163.86   13.295%   $185.6452   $185.65   $185.65   $185.60  
  Purchase #6 $178.98   9.286%   $195.6001   $195.60   $195.60   $195.60  
  Purchase #7 $143.69   11.733%   $160.5491   $160.55   $160.55   $160.50  
  7 purchase totals = $1,135.76       $1,254.2531   $1,254.26   $1,254.25   $1,254.20