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 $185.42   12.194%   $208.0301   $208.03   $208.05   $208.00  
  Purchase #2 $221.66   8.842%   $241.2592   $241.26   $241.25   $241.30  
  Purchase #3 $25.44   8.365%   $27.5681   $27.57   $27.55   $27.60  
  Purchase #4 $223.42   13.808%   $254.2698   $254.27   $254.25   $254.30  
  Purchase #5 $78.68   9.529%   $86.1774   $86.18   $86.20   $86.20  
  Purchase #6 $97.99   4.728%   $102.623   $102.62   $102.60   $102.60  
  Purchase #7 $232.88   9.500%   $255.0036   $255.00   $255.00   $255.00  
  7 purchase totals = $1,065.49       $1,174.9312   $1,174.93   $1,174.90   $1,175.00