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 $178.91   11.814%   $200.0464   $200.05   $200.05   $200.00  
  Purchase #2 $139.26   6.364%   $148.1225   $148.12   $148.10   $148.10  
  Purchase #3 $45.89   6.365%   $48.8109   $48.81   $48.80   $48.80  
  Purchase #4 $60.66   4.758%   $63.5462   $63.55   $63.55   $63.50  
  Purchase #5 $29.74   11.847%   $33.2633   $33.26   $33.25   $33.30  
  Purchase #6 $227.48   9.243%   $248.506   $248.51   $248.50   $248.50  
  Purchase #7 $16.37   5.436%   $17.2599   $17.26   $17.25   $17.30  
  7 purchase totals = $698.31       $759.5552   $759.56   $759.50   $759.50