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 $165.69   11.108%   $184.0948   $184.09   $184.10   $184.10  
  Purchase #2 $67.61   3.108%   $69.7113   $69.71   $69.70   $69.70  
  Purchase #3 $180.25   4.438%   $188.2495   $188.25   $188.25   $188.20  
  Purchase #4 $57.30   9.295%   $62.626   $62.63   $62.65   $62.60  
  Purchase #5 $211.66   10.665%   $234.2335   $234.23   $234.25   $234.20  
  Purchase #6 $18.57   8.277%   $20.107   $20.11   $20.10   $20.10  
  Purchase #7 $127.63   11.450%   $142.2436   $142.24   $142.25   $142.20  
  7 purchase totals = $828.71       $901.2657   $901.26   $901.30   $901.10