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 $250.94   5.721%   $265.2963   $265.30   $265.30   $265.30  
  Purchase #2 $80.88   6.635%   $86.2464   $86.25   $86.25   $86.20  
  Purchase #3 $248.49   9.781%   $272.7948   $272.79   $272.80   $272.80  
  Purchase #4 $36.47   13.581%   $41.423   $41.42   $41.40   $41.40  
  Purchase #5 $163.38   6.326%   $173.7154   $173.72   $173.70   $173.70  
  Purchase #6 $51.78   5.173%   $54.4586   $54.46   $54.45   $54.50  
  Purchase #7 $177.69   3.587%   $184.0637   $184.06   $184.05   $184.10  
  7 purchase totals = $1,009.63       $1,077.9982   $1,078.00   $1,077.95   $1,078.00