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 $208.53   5.817%   $220.6602   $220.66   $220.65   $220.70  
  Purchase #2 $184.95   5.765%   $195.6124   $195.61   $195.60   $195.60  
  Purchase #3 $19.30   11.262%   $21.4736   $21.47   $21.45   $21.50  
  Purchase #4 $84.76   6.489%   $90.2601   $90.26   $90.25   $90.30  
  Purchase #5 $217.45   8.374%   $235.6593   $235.66   $235.65   $235.70  
  Purchase #6 $56.89   4.427%   $59.4085   $59.41   $59.40   $59.40  
  Purchase #7 $162.81   7.636%   $175.2422   $175.24   $175.25   $175.20  
  7 purchase totals = $934.69       $998.3163   $998.31   $998.25   $998.40