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 $69.59   8.256%   $75.3354   $75.34   $75.35   $75.30  
  Purchase #2 $140.38   9.790%   $154.1232   $154.12   $154.10   $154.10  
  Purchase #3 $176.77   11.147%   $196.4746   $196.47   $196.45   $196.50  
  Purchase #4 $118.88   13.135%   $134.4949   $134.49   $134.50   $134.50  
  Purchase #5 $95.70   8.358%   $103.6986   $103.70   $103.70   $103.70  
  Purchase #6 $32.34   6.508%   $34.4447   $34.44   $34.45   $34.40  
  Purchase #7 $235.36   11.234%   $261.8003   $261.80   $261.80   $261.80  
  7 purchase totals = $869.02       $960.3717   $960.36   $960.35   $960.30