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 $247.41   5.601%   $261.2674   $261.27   $261.25   $261.30  
  Purchase #2 $116.93   9.125%   $127.5999   $127.60   $127.60   $127.60  
  Purchase #3 $180.96   11.856%   $202.4146   $202.41   $202.40   $202.40  
  Purchase #4 $218.74   8.351%   $237.007   $237.01   $237.00   $237.00  
  Purchase #5 $168.70   8.575%   $183.166   $183.17   $183.15   $183.20  
  Purchase #6 $242.30   3.467%   $250.7005   $250.70   $250.70   $250.70  
  Purchase #7 $98.30   11.297%   $109.405   $109.41   $109.40   $109.40  
  7 purchase totals = $1,273.34       $1,371.5604   $1,371.57   $1,371.50   $1,371.60