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 $82.69   13.850%   $94.1426   $94.14   $94.15   $94.10  
  Purchase #2 $78.99   4.766%   $82.7547   $82.75   $82.75   $82.80  
  Purchase #3 $190.90   11.353%   $212.5729   $212.57   $212.55   $212.60  
  Purchase #4 $163.64   9.564%   $179.2905   $179.29   $179.30   $179.30  
  Purchase #5 $101.61   7.806%   $109.5417   $109.54   $109.55   $109.50  
  Purchase #6 $203.70   11.555%   $227.2375   $227.24   $227.25   $227.20  
  Purchase #7 $51.77   11.660%   $57.8064   $57.81   $57.80   $57.80  
  7 purchase totals = $873.30       $963.3463   $963.34   $963.35   $963.30