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 $144.26   3.826%   $149.7794   $149.78   $149.80   $149.80  
  Purchase #2 $175.50   10.393%   $193.7397   $193.74   $193.75   $193.70  
  Purchase #3 $76.67   3.231%   $79.1472   $79.15   $79.15   $79.10  
  Purchase #4 $109.69   11.655%   $122.4744   $122.47   $122.45   $122.50  
  Purchase #5 $94.78   12.111%   $106.2588   $106.26   $106.25   $106.30  
  Purchase #6 $200.45   5.587%   $211.6491   $211.65   $211.65   $211.60  
  Purchase #7 $228.97   9.430%   $250.5619   $250.56   $250.55   $250.60  
  7 purchase totals = $1,030.32       $1,113.6105   $1,113.61   $1,113.60   $1,113.60