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 $248.39   3.159%   $256.2366   $256.24   $256.25   $256.20  
  Purchase #2 $127.68   11.519%   $142.3875   $142.39   $142.40   $142.40  
  Purchase #3 $30.25   11.346%   $33.6822   $33.68   $33.70   $33.70  
  Purchase #4 $23.91   13.391%   $27.1118   $27.11   $27.10   $27.10  
  Purchase #5 $110.44   4.856%   $115.803   $115.80   $115.80   $115.80  
  Purchase #6 $161.74   4.205%   $168.5412   $168.54   $168.55   $168.50  
  Purchase #7 $201.62   10.368%   $222.524   $222.52   $222.50   $222.50  
  7 purchase totals = $904.03       $966.2863   $966.28   $966.30   $966.20