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 $213.84   8.577%   $232.1811   $232.18   $232.20   $232.20  
  Purchase #2 $71.93   4.254%   $74.9899   $74.99   $75.00   $75.00  
  Purchase #3 $87.25   6.719%   $93.1123   $93.11   $93.10   $93.10  
  Purchase #4 $60.28   8.546%   $65.4315   $65.43   $65.45   $65.40  
  Purchase #5 $126.30   10.441%   $139.487   $139.49   $139.50   $139.50  
  Purchase #6 $86.77   5.661%   $91.682   $91.68   $91.70   $91.70  
  Purchase #7 $26.73   13.262%   $30.2749   $30.27   $30.25   $30.30  
  7 purchase totals = $673.10       $727.1587   $727.15   $727.20   $727.20