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 $59.86   4.116%   $62.3238   $62.32   $62.30   $62.30  
  Purchase #2 $20.41   6.315%   $21.6989   $21.70   $21.70   $21.70  
  Purchase #3 $222.88   8.216%   $241.1918   $241.19   $241.20   $241.20  
  Purchase #4 $37.40   11.856%   $41.8341   $41.83   $41.85   $41.80  
  Purchase #5 $151.57   6.839%   $161.9359   $161.94   $161.95   $161.90  
  Purchase #6 $44.31   5.346%   $46.6788   $46.68   $46.70   $46.70  
  Purchase #7 $217.69   4.190%   $226.8112   $226.81   $226.80   $226.80  
  7 purchase totals = $754.12       $802.4745   $802.47   $802.50   $802.40