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 $33.38   6.729%   $35.6261   $35.63   $35.65   $35.60  
  Purchase #2 $247.34   10.387%   $273.0312   $273.03   $273.05   $273.00  
  Purchase #3 $184.89   12.582%   $208.1529   $208.15   $208.15   $208.20  
  Purchase #4 $11.32   9.104%   $12.3506   $12.35   $12.35   $12.40  
  Purchase #5 $192.50   4.712%   $201.5706   $201.57   $201.55   $201.60  
  Purchase #6 $82.64   5.134%   $86.8827   $86.88   $86.90   $86.90  
  Purchase #7 $176.65   9.723%   $193.8257   $193.83   $193.85   $193.80  
  7 purchase totals = $928.72       $1,011.4398   $1,011.44   $1,011.50   $1,011.50