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 $193.88   10.702%   $214.629   $214.63   $214.65   $214.60  
  Purchase #2 $10.66   3.303%   $11.0121   $11.01   $11.00   $11.00  
  Purchase #3 $121.72   4.345%   $127.0087   $127.01   $127.00   $127.00  
  Purchase #4 $244.85   7.109%   $262.2564   $262.26   $262.25   $262.30  
  Purchase #5 $245.79   3.659%   $254.7835   $254.78   $254.80   $254.80  
  Purchase #6 $164.85   5.518%   $173.9464   $173.95   $173.95   $173.90  
  Purchase #7 $222.58   6.569%   $237.2013   $237.20   $237.20   $237.20  
  7 purchase totals = $1,204.33       $1,280.8374   $1,280.84   $1,280.85   $1,280.80