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 $39.61   9.627%   $43.4233   $43.42   $43.40   $43.40  
  Purchase #2 $190.63   12.759%   $214.9525   $214.95   $214.95   $215.00  
  Purchase #3 $23.53   6.581%   $25.0785   $25.08   $25.10   $25.10  
  Purchase #4 $152.53   13.769%   $173.5319   $173.53   $173.55   $173.50  
  Purchase #5 $178.29   11.509%   $198.8094   $198.81   $198.80   $198.80  
  Purchase #6 $170.67   13.321%   $193.405   $193.41   $193.40   $193.40  
  Purchase #7 $110.79   3.255%   $114.3962   $114.40   $114.40   $114.40  
  7 purchase totals = $866.05       $963.5968   $963.60   $963.60   $963.60