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 $161.61   13.804%   $183.9186   $183.92   $183.90   $183.90  
  Purchase #2 $208.41   6.197%   $221.3252   $221.33   $221.35   $221.30  
  Purchase #3 $230.53   13.390%   $261.398   $261.40   $261.40   $261.40  
  Purchase #4 $235.97   13.250%   $267.236   $267.24   $267.25   $267.20  
  Purchase #5 $215.97   12.103%   $242.1088   $242.11   $242.10   $242.10  
  Purchase #6 $172.85   6.313%   $183.762   $183.76   $183.75   $183.80  
  Purchase #7 $217.77   6.780%   $232.5348   $232.53   $232.55   $232.50  
  7 purchase totals = $1,443.11       $1,592.2834   $1,592.29   $1,592.30   $1,592.20