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 $56.69   13.758%   $64.4894   $64.49   $64.50   $64.50  
  Purchase #2 $214.49   10.510%   $237.0329   $237.03   $237.05   $237.00  
  Purchase #3 $93.51   9.596%   $102.4832   $102.48   $102.50   $102.50  
  Purchase #4 $161.63   3.259%   $166.8975   $166.90   $166.90   $166.90  
  Purchase #5 $250.28   5.720%   $264.596   $264.60   $264.60   $264.60  
  Purchase #6 $180.85   3.322%   $186.8578   $186.86   $186.85   $186.90  
  Purchase #7 $238.38   8.718%   $259.162   $259.16   $259.15   $259.20  
  7 purchase totals = $1,195.83       $1,281.5188   $1,281.52   $1,281.55   $1,281.60