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 $48.41   6.138%   $51.3814   $51.38   $51.40   $51.40  
  Purchase #2 $56.31   7.780%   $60.6909   $60.69   $60.70   $60.70  
  Purchase #3 $57.77   9.157%   $63.06   $63.06   $63.05   $63.10  
  Purchase #4 $163.49   7.187%   $175.24   $175.24   $175.25   $175.20  
  Purchase #5 $103.76   10.233%   $114.3778   $114.38   $114.40   $114.40  
  Purchase #6 $232.60   7.760%   $250.6498   $250.65   $250.65   $250.60  
  Purchase #7 $36.60   6.270%   $38.8948   $38.89   $38.90   $38.90  
  7 purchase totals = $698.94       $754.2947   $754.29   $754.35   $754.30