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 $238.98   9.863%   $262.5506   $262.55   $262.55   $262.60  
  Purchase #2 $193.99   8.517%   $210.5121   $210.51   $210.50   $210.50  
  Purchase #3 $239.38   5.384%   $252.2682   $252.27   $252.25   $252.30  
  Purchase #4 $87.89   10.421%   $97.049   $97.05   $97.05   $97.00  
  Purchase #5 $72.90   5.832%   $77.1515   $77.15   $77.15   $77.20  
  Purchase #6 $230.72   6.647%   $246.056   $246.06   $246.05   $246.10  
  Purchase #7 $114.69   7.439%   $123.2218   $123.22   $123.20   $123.20  
  7 purchase totals = $1,178.55       $1,268.8092   $1,268.81   $1,268.75   $1,268.90