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 $103.54   13.562%   $117.5821   $117.58   $117.60   $117.60  
  Purchase #2 $71.26   4.448%   $74.4296   $74.43   $74.45   $74.40  
  Purchase #3 $95.98   7.536%   $103.2131   $103.21   $103.20   $103.20  
  Purchase #4 $86.68   4.675%   $90.7323   $90.73   $90.75   $90.70  
  Purchase #5 $203.80   5.308%   $214.6177   $214.62   $214.60   $214.60  
  Purchase #6 $176.80   9.292%   $193.2283   $193.23   $193.25   $193.20  
  Purchase #7 $245.98   6.613%   $262.2467   $262.25   $262.25   $262.20  
  7 purchase totals = $984.04       $1,056.0498   $1,056.05   $1,056.10   $1,055.90