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 $61.63   4.844%   $64.6154   $64.62   $64.60   $64.60  
  Purchase #2 $161.71   9.582%   $177.2051   $177.21   $177.20   $177.20  
  Purchase #3 $79.38   4.172%   $82.6917   $82.69   $82.70   $82.70  
  Purchase #4 $205.38   3.187%   $211.9255   $211.93   $211.95   $211.90  
  Purchase #5 $192.91   4.828%   $202.2237   $202.22   $202.20   $202.20  
  Purchase #6 $152.54   6.469%   $162.4078   $162.41   $162.40   $162.40  
  Purchase #7 $228.82   4.255%   $238.5563   $238.56   $238.55   $238.60  
  7 purchase totals = $1,082.37       $1,139.6255   $1,139.64   $1,139.60   $1,139.60