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 $58.57   11.615%   $65.3729   $65.37   $65.35   $65.40  
  Purchase #2 $183.77   10.396%   $202.8747   $202.87   $202.85   $202.90  
  Purchase #3 $115.34   7.842%   $124.385   $124.39   $124.40   $124.40  
  Purchase #4 $151.64   8.509%   $164.543   $164.54   $164.55   $164.50  
  Purchase #5 $34.96   6.426%   $37.2065   $37.21   $37.20   $37.20  
  Purchase #6 $117.71   6.391%   $125.2328   $125.23   $125.25   $125.20  
  Purchase #7 $206.90   13.502%   $234.8356   $234.84   $234.85   $234.80  
  7 purchase totals = $868.89       $954.4505   $954.45   $954.45   $954.40