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 $200.27   7.346%   $214.9818   $214.98   $215.00   $215.00  
  Purchase #2 $153.83   12.184%   $172.5726   $172.57   $172.55   $172.60  
  Purchase #3 $207.37   12.108%   $232.4784   $232.48   $232.50   $232.50  
  Purchase #4 $248.67   10.337%   $274.375   $274.38   $274.40   $274.40  
  Purchase #5 $52.85   7.381%   $56.7509   $56.75   $56.75   $56.80  
  Purchase #6 $87.70   8.643%   $95.2799   $95.28   $95.30   $95.30  
  Purchase #7 $216.93   4.715%   $227.1582   $227.16   $227.15   $227.20  
  7 purchase totals = $1,167.62       $1,273.5968   $1,273.60   $1,273.65   $1,273.80