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 $228.38   11.215%   $253.9928   $253.99   $254.00   $254.00  
  Purchase #2 $60.39   10.192%   $66.5449   $66.54   $66.55   $66.50  
  Purchase #3 $45.50   8.409%   $49.3261   $49.33   $49.35   $49.30  
  Purchase #4 $41.28   5.163%   $43.4113   $43.41   $43.40   $43.40  
  Purchase #5 $186.88   11.548%   $208.4609   $208.46   $208.45   $208.50  
  Purchase #6 $236.32   5.475%   $249.2585   $249.26   $249.25   $249.30  
  Purchase #7 $153.62   4.454%   $160.4622   $160.46   $160.45   $160.50  
  7 purchase totals = $952.37       $1,031.4567   $1,031.45   $1,031.45   $1,031.50