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 $248.96   5.537%   $262.7449   $262.74   $262.75   $262.70  
  Purchase #2 $142.38   11.114%   $158.2041   $158.20   $158.20   $158.20  
  Purchase #3 $13.67   3.616%   $14.1643   $14.16   $14.15   $14.20  
  Purchase #4 $202.77   11.804%   $226.705   $226.71   $226.70   $226.70  
  Purchase #5 $119.25   8.323%   $129.1752   $129.18   $129.20   $129.20  
  Purchase #6 $83.98   6.611%   $89.5319   $89.53   $89.55   $89.50  
  Purchase #7 $153.58   9.811%   $168.6477   $168.65   $168.65   $168.60  
  7 purchase totals = $964.59       $1,049.1731   $1,049.17   $1,049.20   $1,049.10