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 $95.41   3.106%   $98.3734   $98.37   $98.35   $98.40  
  Purchase #2 $73.59   11.817%   $82.2861   $82.29   $82.30   $82.30  
  Purchase #3 $227.70   10.703%   $252.0707   $252.07   $252.05   $252.10  
  Purchase #4 $89.41   12.123%   $100.2492   $100.25   $100.25   $100.20  
  Purchase #5 $24.79   7.447%   $26.6361   $26.64   $26.65   $26.60  
  Purchase #6 $167.51   10.841%   $185.6698   $185.67   $185.65   $185.70  
  Purchase #7 $250.64   9.318%   $273.9946   $273.99   $274.00   $274.00  
  7 purchase totals = $929.05       $1,019.2799   $1,019.28   $1,019.25   $1,019.30