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 $34.73   4.821%   $36.4043   $36.40   $36.40   $36.40  
  Purchase #2 $105.38   5.602%   $111.2834   $111.28   $111.30   $111.30  
  Purchase #3 $170.46   13.608%   $193.6562   $193.66   $193.65   $193.70  
  Purchase #4 $214.99   10.478%   $237.5167   $237.52   $237.50   $237.50  
  Purchase #5 $26.74   4.284%   $27.8855   $27.89   $27.90   $27.90  
  Purchase #6 $232.44   4.505%   $242.9114   $242.91   $242.90   $242.90  
  Purchase #7 $215.88   5.131%   $226.9568   $226.96   $226.95   $227.00  
  7 purchase totals = $1,000.62       $1,076.6143   $1,076.62   $1,076.60   $1,076.70