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 $134.61   8.653%   $146.2578   $146.26   $146.25   $146.30  
  Purchase #2 $152.50   7.277%   $163.5974   $163.60   $163.60   $163.60  
  Purchase #3 $208.93   4.831%   $219.0234   $219.02   $219.00   $219.00  
  Purchase #4 $119.46   4.807%   $125.2024   $125.20   $125.20   $125.20  
  Purchase #5 $247.33   3.762%   $256.6346   $256.63   $256.65   $256.60  
  Purchase #6 $151.58   3.291%   $156.5685   $156.57   $156.55   $156.60  
  Purchase #7 $147.49   11.746%   $164.8142   $164.81   $164.80   $164.80  
  7 purchase totals = $1,161.90       $1,232.0983   $1,232.09   $1,232.05   $1,232.10