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 $49.40   8.545%   $53.6212   $53.62   $53.60   $53.60  
  Purchase #2 $167.97   4.189%   $175.0063   $175.01   $175.00   $175.00  
  Purchase #3 $234.64   8.142%   $253.7444   $253.74   $253.75   $253.70  
  Purchase #4 $229.93   9.637%   $252.0884   $252.09   $252.10   $252.10  
  Purchase #5 $65.45   8.737%   $71.1684   $71.17   $71.15   $71.20  
  Purchase #6 $113.87   4.629%   $119.141   $119.14   $119.15   $119.10  
  Purchase #7 $30.91   12.215%   $34.6857   $34.69   $34.70   $34.70  
  7 purchase totals = $892.17       $959.4554   $959.46   $959.45   $959.40