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 $24.88   7.362%   $26.7117   $26.71   $26.70   $26.70  
  Purchase #2 $86.25   10.553%   $95.352   $95.35   $95.35   $95.40  
  Purchase #3 $114.49   5.143%   $120.3782   $120.38   $120.40   $120.40  
  Purchase #4 $26.67   10.333%   $29.4258   $29.43   $29.45   $29.40  
  Purchase #5 $180.83   9.430%   $197.8823   $197.88   $197.90   $197.90  
  Purchase #6 $170.58   9.799%   $187.2951   $187.30   $187.30   $187.30  
  Purchase #7 $161.37   4.719%   $168.9851   $168.99   $169.00   $169.00  
  7 purchase totals = $765.07       $826.0302   $826.04   $826.10   $826.10