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 $160.78   9.652%   $176.2985   $176.30   $176.30   $176.30  
  Purchase #2 $144.75   8.155%   $156.5544   $156.55   $156.55   $156.60  
  Purchase #3 $32.62   12.118%   $36.5729   $36.57   $36.55   $36.60  
  Purchase #4 $228.91   10.696%   $253.3942   $253.39   $253.40   $253.40  
  Purchase #5 $169.83   5.260%   $178.7631   $178.76   $178.75   $178.80  
  Purchase #6 $73.87   7.660%   $79.5284   $79.53   $79.55   $79.50  
  Purchase #7 $154.54   5.184%   $162.5514   $162.55   $162.55   $162.60  
  7 purchase totals = $965.30       $1,043.6629   $1,043.65   $1,043.65   $1,043.80