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 $227.69   13.465%   $258.3485   $258.35   $258.35   $258.30  
  Purchase #2 $117.54   8.273%   $127.2641   $127.26   $127.25   $127.30  
  Purchase #3 $230.72   3.737%   $239.342   $239.34   $239.35   $239.30  
  Purchase #4 $119.46   8.451%   $129.5556   $129.56   $129.55   $129.60  
  Purchase #5 $237.67   3.220%   $245.323   $245.32   $245.30   $245.30  
  Purchase #6 $69.83   4.847%   $73.2147   $73.21   $73.20   $73.20  
  Purchase #7 $113.26   8.665%   $123.074   $123.07   $123.05   $123.10  
  7 purchase totals = $1,116.17       $1,196.1219   $1,196.11   $1,196.05   $1,196.10