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 $244.29   5.157%   $256.888   $256.89   $256.90   $256.90  
  Purchase #2 $249.46   10.771%   $276.3293   $276.33   $276.35   $276.30  
  Purchase #3 $33.58   5.335%   $35.3715   $35.37   $35.35   $35.40  
  Purchase #4 $78.65   8.672%   $85.4705   $85.47   $85.45   $85.50  
  Purchase #5 $176.60   5.391%   $186.1205   $186.12   $186.10   $186.10  
  Purchase #6 $208.86   13.470%   $236.9934   $236.99   $237.00   $237.00  
  Purchase #7 $161.25   5.480%   $170.0865   $170.09   $170.10   $170.10  
  7 purchase totals = $1,152.69       $1,247.2597   $1,247.26   $1,247.25   $1,247.30