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 $143.64   10.250%   $158.3631   $158.36   $158.35   $158.40  
  Purchase #2 $190.82   13.245%   $216.0941   $216.09   $216.10   $216.10  
  Purchase #3 $7.58   10.418%   $8.3697   $8.37   $8.35   $8.40  
  Purchase #4 $18.26   4.819%   $19.1399   $19.14   $19.15   $19.10  
  Purchase #5 $26.91   10.826%   $29.8233   $29.82   $29.80   $29.80  
  Purchase #6 $152.81   7.173%   $163.7711   $163.77   $163.75   $163.80  
  Purchase #7 $182.38   3.464%   $188.6976   $188.70   $188.70   $188.70  
  7 purchase totals = $722.40       $784.2588   $784.25   $784.20   $784.30