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 $212.69   13.580%   $241.5733   $241.57   $241.55   $241.60  
  Purchase #2 $141.86   7.574%   $152.6045   $152.60   $152.60   $152.60  
  Purchase #3 $81.88   7.585%   $88.0906   $88.09   $88.10   $88.10  
  Purchase #4 $76.49   13.105%   $86.514   $86.51   $86.50   $86.50  
  Purchase #5 $144.33   7.860%   $155.6743   $155.67   $155.65   $155.70  
  Purchase #6 $120.37   6.738%   $128.4805   $128.48   $128.50   $128.50  
  Purchase #7 $176.63   9.656%   $193.6854   $193.69   $193.70   $193.70  
  7 purchase totals = $954.25       $1,046.6226   $1,046.61   $1,046.60   $1,046.70