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 $211.96   12.294%   $238.0184   $238.02   $238.00   $238.00  
  Purchase #2 $55.84   3.626%   $57.8648   $57.86   $57.85   $57.90  
  Purchase #3 $13.86   7.433%   $14.8902   $14.89   $14.90   $14.90  
  Purchase #4 $102.28   3.814%   $106.181   $106.18   $106.20   $106.20  
  Purchase #5 $124.32   5.367%   $130.9923   $130.99   $131.00   $131.00  
  Purchase #6 $144.92   6.536%   $154.392   $154.39   $154.40   $154.40  
  Purchase #7 $214.97   3.502%   $222.4982   $222.50   $222.50   $222.50  
  7 purchase totals = $868.15       $924.8369   $924.83   $924.85   $924.90