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 $213.69   11.364%   $237.9737   $237.97   $237.95   $238.00  
  Purchase #2 $174.76   13.252%   $197.9192   $197.92   $197.90   $197.90  
  Purchase #3 $130.51   5.868%   $138.1683   $138.17   $138.15   $138.20  
  Purchase #4 $44.64   5.448%   $47.072   $47.07   $47.05   $47.10  
  Purchase #5 $12.57   5.293%   $13.2353   $13.24   $13.25   $13.20  
  Purchase #6 $103.89   13.137%   $117.538   $117.54   $117.55   $117.50  
  Purchase #7 $250.85   7.621%   $269.9673   $269.97   $269.95   $270.00  
  7 purchase totals = $930.91       $1,021.8738   $1,021.88   $1,021.80   $1,021.90