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 $208.78   7.657%   $224.7663   $224.77   $224.75   $224.80  
  Purchase #2 $127.64   11.116%   $141.8285   $141.83   $141.85   $141.80  
  Purchase #3 $231.37   7.798%   $249.4122   $249.41   $249.40   $249.40  
  Purchase #4 $24.70   5.650%   $26.0956   $26.10   $26.10   $26.10  
  Purchase #5 $115.58   8.428%   $125.3211   $125.32   $125.30   $125.30  
  Purchase #6 $41.54   5.195%   $43.698   $43.70   $43.70   $43.70  
  Purchase #7 $221.69   13.642%   $251.9329   $251.93   $251.95   $251.90  
  7 purchase totals = $971.30       $1,063.0546   $1,063.06   $1,063.05   $1,063.00