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 $240.33   10.871%   $266.4563   $266.46   $266.45   $266.50  
  Purchase #2 $214.81   6.656%   $229.1078   $229.11   $229.10   $229.10  
  Purchase #3 $227.47   5.823%   $240.7156   $240.72   $240.70   $240.70  
  Purchase #4 $129.26   11.667%   $144.3408   $144.34   $144.35   $144.30  
  Purchase #5 $161.99   3.255%   $167.2628   $167.26   $167.25   $167.30  
  Purchase #6 $152.86   8.843%   $166.3774   $166.38   $166.40   $166.40  
  Purchase #7 $11.74   11.522%   $13.0927   $13.09   $13.10   $13.10  
  7 purchase totals = $1,138.46       $1,227.3534   $1,227.36   $1,227.35   $1,227.40