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 $58.63   13.546%   $66.572   $66.57   $66.55   $66.60  
  Purchase #2 $151.45   8.593%   $164.4641   $164.46   $164.45   $164.50  
  Purchase #3 $115.34   11.864%   $129.0239   $129.02   $129.00   $129.00  
  Purchase #4 $82.46   3.564%   $85.3989   $85.40   $85.40   $85.40  
  Purchase #5 $165.63   3.267%   $171.0411   $171.04   $171.05   $171.00  
  Purchase #6 $166.43   11.135%   $184.962   $184.96   $184.95   $185.00  
  Purchase #7 $60.53   9.571%   $66.3233   $66.32   $66.30   $66.30  
  7 purchase totals = $800.47       $867.7853   $867.77   $867.70   $867.80