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 $50.61   11.789%   $56.5764   $56.58   $56.60   $56.60  
  Purchase #2 $168.90   5.277%   $177.8129   $177.81   $177.80   $177.80  
  Purchase #3 $29.37   8.591%   $31.8932   $31.89   $31.90   $31.90  
  Purchase #4 $33.37   5.287%   $35.1343   $35.13   $35.15   $35.10  
  Purchase #5 $115.82   8.559%   $125.733   $125.73   $125.75   $125.70  
  Purchase #6 $236.85   13.765%   $269.4524   $269.45   $269.45   $269.50  
  Purchase #7 $55.78   3.832%   $57.9175   $57.92   $57.90   $57.90  
  7 purchase totals = $690.70       $754.5197   $754.51   $754.55   $754.50