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 $114.25   11.688%   $127.6035   $127.60   $127.60   $127.60  
  Purchase #2 $227.68   13.457%   $258.3189   $258.32   $258.30   $258.30  
  Purchase #3 $163.28   7.805%   $176.024   $176.02   $176.00   $176.00  
  Purchase #4 $25.85   7.567%   $27.8061   $27.81   $27.80   $27.80  
  Purchase #5 $57.83   5.587%   $61.061   $61.06   $61.05   $61.10  
  Purchase #6 $229.72   6.857%   $245.4719   $245.47   $245.45   $245.50  
  Purchase #7 $245.90   9.807%   $270.0154   $270.02   $270.00   $270.00  
  7 purchase totals = $1,064.51       $1,166.3008   $1,166.30   $1,166.20   $1,166.30