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 $241.58   10.333%   $266.5425   $266.54   $266.55   $266.50  
  Purchase #2 $201.53   4.277%   $210.1494   $210.15   $210.15   $210.10  
  Purchase #3 $109.91   12.260%   $123.385   $123.39   $123.40   $123.40  
  Purchase #4 $32.97   13.274%   $37.3464   $37.35   $37.35   $37.30  
  Purchase #5 $180.67   9.400%   $197.653   $197.65   $197.65   $197.70  
  Purchase #6 $58.26   3.141%   $60.0899   $60.09   $60.10   $60.10  
  Purchase #7 $227.70   4.193%   $237.2475   $237.25   $237.25   $237.20  
  7 purchase totals = $1,052.62       $1,132.4137   $1,132.42   $1,132.45   $1,132.30