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 $7.40   4.129%   $7.7055   $7.71   $7.70   $7.70  
  Purchase #2 $178.33   11.467%   $198.7791   $198.78   $198.80   $198.80  
  Purchase #3 $44.67   12.577%   $50.2881   $50.29   $50.30   $50.30  
  Purchase #4 $100.83   3.512%   $104.3711   $104.37   $104.35   $104.40  
  Purchase #5 $86.38   10.537%   $95.4819   $95.48   $95.50   $95.50  
  Purchase #6 $150.66   13.708%   $171.3125   $171.31   $171.30   $171.30  
  Purchase #7 $197.40   8.569%   $214.3152   $214.32   $214.30   $214.30  
  7 purchase totals = $765.67       $842.2534   $842.26   $842.25   $842.30