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 $9.93   4.449%   $10.3718   $10.37   $10.35   $10.40  
  Purchase #2 $190.59   11.344%   $212.2105   $212.21   $212.20   $212.20  
  Purchase #3 $100.61   4.176%   $104.8115   $104.81   $104.80   $104.80  
  Purchase #4 $208.35   10.688%   $230.6184   $230.62   $230.60   $230.60  
  Purchase #5 $179.44   7.306%   $192.5499   $192.55   $192.55   $192.50  
  Purchase #6 $169.33   10.857%   $187.7142   $187.71   $187.70   $187.70  
  Purchase #7 $182.57   8.519%   $198.1231   $198.12   $198.10   $198.10  
  7 purchase totals = $1,040.82       $1,136.3994   $1,136.39   $1,136.30   $1,136.30