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 $144.76   6.484%   $154.1462   $154.15   $154.15   $154.10  
  Purchase #2 $59.30   4.593%   $62.0236   $62.02   $62.00   $62.00  
  Purchase #3 $234.61   8.184%   $253.8105   $253.81   $253.80   $253.80  
  Purchase #4 $183.62   9.671%   $201.3779   $201.38   $201.40   $201.40  
  Purchase #5 $164.33   6.832%   $175.557   $175.56   $175.55   $175.60  
  Purchase #6 $84.60   4.119%   $88.0847   $88.08   $88.10   $88.10  
  Purchase #7 $244.68   6.699%   $261.0711   $261.07   $261.05   $261.10  
  7 purchase totals = $1,115.90       $1,196.0710   $1,196.07   $1,196.05   $1,196.10