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 $213.99   11.706%   $239.0397   $239.04   $239.05   $239.00  
  Purchase #2 $135.81   10.716%   $150.3634   $150.36   $150.35   $150.40  
  Purchase #3 $204.94   13.318%   $232.2339   $232.23   $232.25   $232.20  
  Purchase #4 $216.80   4.672%   $226.9289   $226.93   $226.95   $226.90  
  Purchase #5 $60.34   7.719%   $64.9976   $65.00   $65.00   $65.00  
  Purchase #6 $166.96   6.533%   $177.8675   $177.87   $177.85   $177.90  
  Purchase #7 $210.33   3.870%   $218.4698   $218.47   $218.45   $218.50  
  7 purchase totals = $1,209.17       $1,309.9008   $1,309.90   $1,309.90   $1,309.90