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 $146.61   13.591%   $166.5358   $166.54   $166.55   $166.50  
  Purchase #2 $156.90   12.239%   $176.103   $176.10   $176.10   $176.10  
  Purchase #3 $23.40   11.535%   $26.0992   $26.10   $26.10   $26.10  
  Purchase #4 $122.36   7.666%   $131.7401   $131.74   $131.75   $131.70  
  Purchase #5 $232.85   10.701%   $257.7673   $257.77   $257.75   $257.80  
  Purchase #6 $189.61   5.316%   $199.6897   $199.69   $199.70   $199.70  
  Purchase #7 $109.58   4.661%   $114.6875   $114.69   $114.70   $114.70  
  7 purchase totals = $981.31       $1,072.6226   $1,072.63   $1,072.65   $1,072.60