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 $187.45   11.779%   $209.5297   $209.53   $209.55   $209.50  
  Purchase #2 $73.81   4.268%   $76.9602   $76.96   $76.95   $77.00  
  Purchase #3 $228.33   9.488%   $249.994   $249.99   $250.00   $250.00  
  Purchase #4 $93.95   6.715%   $100.2587   $100.26   $100.25   $100.30  
  Purchase #5 $62.86   3.509%   $65.0658   $65.07   $65.05   $65.10  
  Purchase #6 $155.41   3.759%   $161.2519   $161.25   $161.25   $161.30  
  Purchase #7 $103.81   13.829%   $118.1659   $118.17   $118.15   $118.20  
  7 purchase totals = $905.62       $981.2262   $981.23   $981.20   $981.40