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 $69.30   9.838%   $76.1177   $76.12   $76.10   $76.10  
  Purchase #2 $166.65   4.827%   $174.6942   $174.69   $174.70   $174.70  
  Purchase #3 $238.79   3.261%   $246.5769   $246.58   $246.60   $246.60  
  Purchase #4 $235.71   8.181%   $254.9934   $254.99   $255.00   $255.00  
  Purchase #5 $213.27   12.106%   $239.0885   $239.09   $239.10   $239.10  
  Purchase #6 $238.54   13.859%   $271.5993   $271.60   $271.60   $271.60  
  Purchase #7 $44.73   8.527%   $48.5441   $48.54   $48.55   $48.50  
  7 purchase totals = $1,206.99       $1,311.6141   $1,311.61   $1,311.65   $1,311.60