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 $242.41   5.480%   $255.6941   $255.69   $255.70   $255.70  
  Purchase #2 $14.53   11.239%   $16.163   $16.16   $16.15   $16.20  
  Purchase #3 $172.91   4.531%   $180.7446   $180.74   $180.75   $180.70  
  Purchase #4 $136.35   6.565%   $145.3014   $145.30   $145.30   $145.30  
  Purchase #5 $135.26   6.134%   $143.5568   $143.56   $143.55   $143.60  
  Purchase #6 $247.83   5.722%   $262.0108   $262.01   $262.00   $262.00  
  Purchase #7 $208.94   10.835%   $231.5786   $231.58   $231.60   $231.60  
  7 purchase totals = $1,158.23       $1,235.0493   $1,235.04   $1,235.05   $1,235.10