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 $119.58   10.189%   $131.764   $131.76   $131.75   $131.80  
  Purchase #2 $60.79   13.868%   $69.2204   $69.22   $69.20   $69.20  
  Purchase #3 $222.95   8.157%   $241.136   $241.14   $241.15   $241.10  
  Purchase #4 $151.37   10.680%   $167.5363   $167.54   $167.55   $167.50  
  Purchase #5 $151.74   7.382%   $162.9414   $162.94   $162.95   $162.90  
  Purchase #6 $203.82   9.378%   $222.9342   $222.93   $222.95   $222.90  
  Purchase #7 $247.63   10.124%   $272.7001   $272.70   $272.70   $272.70  
  7 purchase totals = $1,157.88       $1,268.2324   $1,268.23   $1,268.25   $1,268.10