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 $52.71   5.368%   $55.5395   $55.54   $55.55   $55.50  
  Purchase #2 $161.28   7.706%   $173.7082   $173.71   $173.70   $173.70  
  Purchase #3 $145.81   12.220%   $163.628   $163.63   $163.65   $163.60  
  Purchase #4 $25.80   7.482%   $27.7304   $27.73   $27.75   $27.70  
  Purchase #5 $244.39   3.535%   $253.0292   $253.03   $253.05   $253.00  
  Purchase #6 $146.28   5.376%   $154.144   $154.14   $154.15   $154.10  
  Purchase #7 $213.34   8.510%   $231.4952   $231.50   $231.50   $231.50  
  7 purchase totals = $989.61       $1,059.2745   $1,059.28   $1,059.35   $1,059.10