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 $24.97   7.349%   $26.805   $26.81   $26.80   $26.80  
  Purchase #2 $246.75   5.208%   $259.6007   $259.60   $259.60   $259.60  
  Purchase #3 $63.36   9.868%   $69.6124   $69.61   $69.60   $69.60  
  Purchase #4 $114.33   8.327%   $123.8503   $123.85   $123.85   $123.90  
  Purchase #5 $197.76   3.778%   $205.2314   $205.23   $205.25   $205.20  
  Purchase #6 $95.94   6.607%   $102.2788   $102.28   $102.30   $102.30  
  Purchase #7 $159.41   8.540%   $173.0236   $173.02   $173.00   $173.00  
  7 purchase totals = $902.52       $960.4022   $960.40   $960.40   $960.40