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 $53.48   4.863%   $56.0807   $56.08   $56.10   $56.10  
  Purchase #2 $178.89   3.206%   $184.6252   $184.63   $184.65   $184.60  
  Purchase #3 $186.76   13.624%   $212.2042   $212.20   $212.20   $212.20  
  Purchase #4 $201.91   7.522%   $217.0977   $217.10   $217.10   $217.10  
  Purchase #5 $249.57   7.373%   $267.9708   $267.97   $267.95   $268.00  
  Purchase #6 $113.34   6.207%   $120.375   $120.38   $120.40   $120.40  
  Purchase #7 $214.59   3.271%   $221.6092   $221.61   $221.60   $221.60  
  7 purchase totals = $1,198.54       $1,279.9628   $1,279.97   $1,280.00   $1,280.00