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 $248.91   7.673%   $268.0089   $268.01   $268.00   $268.00  
  Purchase #2 $129.74   8.350%   $140.5733   $140.57   $140.55   $140.60  
  Purchase #3 $34.26   7.421%   $36.8024   $36.80   $36.80   $36.80  
  Purchase #4 $171.66   12.256%   $192.6986   $192.70   $192.70   $192.70  
  Purchase #5 $155.36   9.785%   $170.562   $170.56   $170.55   $170.60  
  Purchase #6 $217.81   4.436%   $227.4721   $227.47   $227.45   $227.50  
  Purchase #7 $124.99   11.673%   $139.5801   $139.58   $139.60   $139.60  
  7 purchase totals = $1,082.73       $1,175.6974   $1,175.69   $1,175.65   $1,175.80