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 $178.76   11.596%   $199.489   $199.49   $199.50   $199.50  
  Purchase #2 $76.25   12.289%   $85.6204   $85.62   $85.60   $85.60  
  Purchase #3 $69.66   5.846%   $73.7323   $73.73   $73.75   $73.70  
  Purchase #4 $230.72   10.223%   $254.3065   $254.31   $254.30   $254.30  
  Purchase #5 $183.25   5.727%   $193.7447   $193.74   $193.75   $193.70  
  Purchase #6 $214.72   9.698%   $235.5435   $235.54   $235.55   $235.50  
  Purchase #7 $187.54   3.459%   $194.027   $194.03   $194.05   $194.00  
  7 purchase totals = $1,140.90       $1,236.4634   $1,236.46   $1,236.50   $1,236.30