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 $186.67   8.206%   $201.9881   $201.99   $202.00   $202.00  
  Purchase #2 $9.57   5.461%   $10.0926   $10.09   $10.10   $10.10  
  Purchase #3 $175.76   5.672%   $185.7291   $185.73   $185.75   $185.70  
  Purchase #4 $87.36   13.579%   $99.2226   $99.22   $99.20   $99.20  
  Purchase #5 $127.54   10.559%   $141.0069   $141.01   $141.00   $141.00  
  Purchase #6 $226.95   13.364%   $257.2796   $257.28   $257.30   $257.30  
  Purchase #7 $228.33   8.637%   $248.0509   $248.05   $248.05   $248.10  
  7 purchase totals = $1,042.18       $1,143.3698   $1,143.37   $1,143.40   $1,143.40