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 $236.88   13.148%   $268.025   $268.03   $268.05   $268.00  
  Purchase #2 $114.31   5.176%   $120.2267   $120.23   $120.25   $120.20  
  Purchase #3 $196.30   6.159%   $208.3901   $208.39   $208.40   $208.40  
  Purchase #4 $164.87   6.146%   $175.0029   $175.00   $175.00   $175.00  
  Purchase #5 $56.80   5.573%   $59.9655   $59.97   $59.95   $60.00  
  Purchase #6 $122.44   10.820%   $135.688   $135.69   $135.70   $135.70  
  Purchase #7 $177.44   3.783%   $184.1526   $184.15   $184.15   $184.20  
  7 purchase totals = $1,069.04       $1,151.4508   $1,151.46   $1,151.50   $1,151.50