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 $187.36   11.271%   $208.4773   $208.48   $208.50   $208.50  
  Purchase #2 $118.33   13.442%   $134.2359   $134.24   $134.25   $134.20  
  Purchase #3 $179.28   3.161%   $184.947   $184.95   $184.95   $184.90  
  Purchase #4 $138.30   3.177%   $142.6938   $142.69   $142.70   $142.70  
  Purchase #5 $54.87   11.655%   $61.2651   $61.27   $61.25   $61.30  
  Purchase #6 $119.40   9.462%   $130.6976   $130.70   $130.70   $130.70  
  Purchase #7 $134.65   3.485%   $139.3426   $139.34   $139.35   $139.30  
  7 purchase totals = $932.19       $1,001.6593   $1,001.67   $1,001.70   $1,001.60