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 $248.93   13.531%   $282.6127   $282.61   $282.60   $282.60  
  Purchase #2 $183.60   5.527%   $193.7476   $193.75   $193.75   $193.70  
  Purchase #3 $9.28   10.155%   $10.2224   $10.22   $10.20   $10.20  
  Purchase #4 $58.78   11.330%   $65.4398   $65.44   $65.45   $65.40  
  Purchase #5 $82.96   11.624%   $92.6033   $92.60   $92.60   $92.60  
  Purchase #6 $211.27   11.729%   $236.0499   $236.05   $236.05   $236.00  
  Purchase #7 $114.33   11.452%   $127.4231   $127.42   $127.40   $127.40  
  7 purchase totals = $909.15       $1,008.0988   $1,008.09   $1,008.05   $1,007.90