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 $41.59   7.402%   $44.6685   $44.67   $44.65   $44.70  
  Purchase #2 $237.53   5.413%   $250.3875   $250.39   $250.40   $250.40  
  Purchase #3 $98.39   3.176%   $101.5149   $101.51   $101.50   $101.50  
  Purchase #4 $185.81   7.599%   $199.9297   $199.93   $199.95   $199.90  
  Purchase #5 $41.48   3.206%   $42.8098   $42.81   $42.80   $42.80  
  Purchase #6 $165.69   5.147%   $174.2181   $174.22   $174.20   $174.20  
  Purchase #7 $105.53   10.139%   $116.2297   $116.23   $116.25   $116.20  
  7 purchase totals = $876.02       $929.7582   $929.76   $929.75   $929.70