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 $102.72   11.623%   $114.6591   $114.66   $114.65   $114.70  
  Purchase #2 $143.42   13.821%   $163.2421   $163.24   $163.25   $163.20  
  Purchase #3 $151.96   10.102%   $167.311   $167.31   $167.30   $167.30  
  Purchase #4 $184.80   7.651%   $198.939   $198.94   $198.95   $198.90  
  Purchase #5 $182.80   7.241%   $196.0365   $196.04   $196.05   $196.00  
  Purchase #6 $9.94   10.709%   $11.0045   $11.00   $11.00   $11.00  
  Purchase #7 $96.61   11.462%   $107.6834   $107.68   $107.70   $107.70  
  7 purchase totals = $872.25       $958.8756   $958.87   $958.90   $958.80