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 $233.87   12.422%   $262.9213   $262.92   $262.90   $262.90  
  Purchase #2 $185.39   3.150%   $191.2298   $191.23   $191.25   $191.20  
  Purchase #3 $83.65   3.811%   $86.8379   $86.84   $86.85   $86.80  
  Purchase #4 $179.30   9.442%   $196.2295   $196.23   $196.25   $196.20  
  Purchase #5 $114.70   10.456%   $126.693   $126.69   $126.70   $126.70  
  Purchase #6 $55.27   6.273%   $58.7371   $58.74   $58.75   $58.70  
  Purchase #7 $67.54   3.104%   $69.6364   $69.64   $69.65   $69.60  
  7 purchase totals = $919.72       $992.2850   $992.29   $992.35   $992.10