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 $248.76   13.617%   $282.6336   $282.63   $282.65   $282.60  
  Purchase #2 $218.28   11.644%   $243.6965   $243.70   $243.70   $243.70  
  Purchase #3 $88.36   8.129%   $95.5428   $95.54   $95.55   $95.50  
  Purchase #4 $152.86   12.128%   $171.3989   $171.40   $171.40   $171.40  
  Purchase #5 $20.58   3.290%   $21.2571   $21.26   $21.25   $21.30  
  Purchase #6 $8.68   6.287%   $9.2257   $9.23   $9.25   $9.20  
  Purchase #7 $98.69   13.263%   $111.7793   $111.78   $111.80   $111.80  
  7 purchase totals = $836.21       $935.5339   $935.54   $935.60   $935.50