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 $239.40   3.602%   $248.0232   $248.02   $248.00   $248.00  
  Purchase #2 $242.51   9.849%   $266.3948   $266.39   $266.40   $266.40  
  Purchase #3 $226.56   10.367%   $250.0475   $250.05   $250.05   $250.00  
  Purchase #4 $23.77   8.797%   $25.861   $25.86   $25.85   $25.90  
  Purchase #5 $68.94   9.588%   $75.55   $75.55   $75.55   $75.60  
  Purchase #6 $99.77   5.667%   $105.424   $105.42   $105.40   $105.40  
  Purchase #7 $159.34   10.209%   $175.607   $175.61   $175.60   $175.60  
  7 purchase totals = $1,060.29       $1,146.9075   $1,146.90   $1,146.85   $1,146.90