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 $59.86   5.602%   $63.2134   $63.21   $63.20   $63.20  
  Purchase #2 $37.32   3.131%   $38.4885   $38.49   $38.50   $38.50  
  Purchase #3 $202.46   5.486%   $213.567   $213.57   $213.55   $213.60  
  Purchase #4 $203.83   11.704%   $227.6863   $227.69   $227.70   $227.70  
  Purchase #5 $178.81   12.306%   $200.8144   $200.81   $200.80   $200.80  
  Purchase #6 $16.60   4.531%   $17.3521   $17.35   $17.35   $17.40  
  Purchase #7 $233.60   10.234%   $257.5066   $257.51   $257.50   $257.50  
  7 purchase totals = $932.48       $1,018.6283   $1,018.63   $1,018.60   $1,018.70