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 $58.77   13.327%   $66.6023   $66.60   $66.60   $66.60  
  Purchase #2 $226.61   5.275%   $238.5637   $238.56   $238.55   $238.60  
  Purchase #3 $165.40   6.767%   $176.5926   $176.59   $176.60   $176.60  
  Purchase #4 $125.89   10.577%   $139.2054   $139.21   $139.20   $139.20  
  Purchase #5 $63.98   9.150%   $69.8342   $69.83   $69.85   $69.80  
  Purchase #6 $119.91   3.742%   $124.397   $124.40   $124.40   $124.40  
  Purchase #7 $115.38   12.335%   $129.6121   $129.61   $129.60   $129.60  
  7 purchase totals = $875.94       $944.8073   $944.80   $944.80   $944.80