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 $218.91   13.286%   $247.9944   $247.99   $248.00   $248.00  
  Purchase #2 $222.68   7.222%   $238.7619   $238.76   $238.75   $238.80  
  Purchase #3 $95.34   12.860%   $107.6007   $107.60   $107.60   $107.60  
  Purchase #4 $58.47   4.339%   $61.007   $61.01   $61.00   $61.00  
  Purchase #5 $208.80   3.478%   $216.0621   $216.06   $216.05   $216.10  
  Purchase #6 $179.90   3.652%   $186.4699   $186.47   $186.45   $186.50  
  Purchase #7 $128.36   8.116%   $138.7777   $138.78   $138.80   $138.80  
  7 purchase totals = $1,112.46       $1,196.6737   $1,196.67   $1,196.65   $1,196.80