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 $237.33   13.632%   $269.6828   $269.68   $269.70   $269.70  
  Purchase #2 $143.54   7.392%   $154.1505   $154.15   $154.15   $154.20  
  Purchase #3 $168.32   4.532%   $175.9483   $175.95   $175.95   $175.90  
  Purchase #4 $220.71   9.601%   $241.9004   $241.90   $241.90   $241.90  
  Purchase #5 $77.63   12.537%   $87.3625   $87.36   $87.35   $87.40  
  Purchase #6 $51.51   12.369%   $57.8813   $57.88   $57.90   $57.90  
  Purchase #7 $109.81   5.280%   $115.608   $115.61   $115.60   $115.60  
  7 purchase totals = $1,008.85       $1,102.5338   $1,102.53   $1,102.55   $1,102.60