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 $56.94   6.350%   $60.5557   $60.56   $60.55   $60.60  
  Purchase #2 $217.65   10.708%   $240.956   $240.96   $240.95   $241.00  
  Purchase #3 $36.68   13.709%   $41.7085   $41.71   $41.70   $41.70  
  Purchase #4 $234.73   13.532%   $266.4937   $266.49   $266.50   $266.50  
  Purchase #5 $114.63   8.772%   $124.6853   $124.69   $124.70   $124.70  
  Purchase #6 $242.65   3.754%   $251.7591   $251.76   $251.75   $251.80  
  Purchase #7 $141.54   6.744%   $151.0855   $151.09   $151.10   $151.10  
  7 purchase totals = $1,044.82       $1,137.2438   $1,137.26   $1,137.25   $1,137.40