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 $200.87   3.573%   $208.0471   $208.05   $208.05   $208.00  
  Purchase #2 $147.38   7.324%   $158.1741   $158.17   $158.15   $158.20  
  Purchase #3 $169.56   8.546%   $184.0506   $184.05   $184.05   $184.10  
  Purchase #4 $24.80   13.162%   $28.0642   $28.06   $28.05   $28.10  
  Purchase #5 $204.49   9.247%   $223.3992   $223.40   $223.40   $223.40  
  Purchase #6 $243.75   6.631%   $259.9131   $259.91   $259.90   $259.90  
  Purchase #7 $192.42   6.338%   $204.6156   $204.62   $204.60   $204.60  
  7 purchase totals = $1,183.27       $1,266.2639   $1,266.26   $1,266.20   $1,266.30