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 $85.35   12.477%   $95.9991   $96.00   $96.00   $96.00  
  Purchase #2 $97.94   13.595%   $111.2549   $111.25   $111.25   $111.30  
  Purchase #3 $15.45   4.419%   $16.1327   $16.13   $16.15   $16.10  
  Purchase #4 $67.68   3.512%   $70.0569   $70.06   $70.05   $70.10  
  Purchase #5 $126.45   6.520%   $134.6945   $134.69   $134.70   $134.70  
  Purchase #6 $74.71   10.110%   $82.2632   $82.26   $82.25   $82.30  
  Purchase #7 $22.54   3.118%   $23.2428   $23.24   $23.25   $23.20  
  7 purchase totals = $490.12       $533.6441   $533.63   $533.65   $533.70