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 $177.26   3.252%   $183.0245   $183.02   $183.00   $183.00  
  Purchase #2 $58.92   10.466%   $65.0866   $65.09   $65.10   $65.10  
  Purchase #3 $213.73   13.174%   $241.8868   $241.89   $241.90   $241.90  
  Purchase #4 $169.46   3.420%   $175.2555   $175.26   $175.25   $175.30  
  Purchase #5 $248.32   13.756%   $282.4789   $282.48   $282.50   $282.50  
  Purchase #6 $19.56   4.870%   $20.5126   $20.51   $20.50   $20.50  
  Purchase #7 $126.59   9.709%   $138.8806   $138.88   $138.90   $138.90  
  7 purchase totals = $1,013.84       $1,107.1255   $1,107.13   $1,107.15   $1,107.20