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 $141.82   8.337%   $153.6435   $153.64   $153.65   $153.60  
  Purchase #2 $219.55   7.759%   $236.5849   $236.58   $236.60   $236.60  
  Purchase #3 $85.80   8.389%   $92.9978   $93.00   $93.00   $93.00  
  Purchase #4 $134.57   8.604%   $146.1484   $146.15   $146.15   $146.10  
  Purchase #5 $208.29   8.724%   $226.4612   $226.46   $226.45   $226.50  
  Purchase #6 $166.76   11.856%   $186.5311   $186.53   $186.55   $186.50  
  Purchase #7 $242.32   3.325%   $250.3771   $250.38   $250.40   $250.40  
  7 purchase totals = $1,199.11       $1,292.7440   $1,292.74   $1,292.80   $1,292.70