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 $206.59   13.283%   $234.0313   $234.03   $234.05   $234.00  
  Purchase #2 $157.43   11.435%   $175.4321   $175.43   $175.45   $175.40  
  Purchase #3 $58.80   13.571%   $66.7797   $66.78   $66.80   $66.80  
  Purchase #4 $69.95   5.137%   $73.5433   $73.54   $73.55   $73.50  
  Purchase #5 $29.25   3.460%   $30.2621   $30.26   $30.25   $30.30  
  Purchase #6 $167.37   3.193%   $172.7141   $172.71   $172.70   $172.70  
  Purchase #7 $205.27   3.790%   $213.0497   $213.05   $213.05   $213.00  
  7 purchase totals = $894.66       $965.8123   $965.80   $965.85   $965.70