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 $59.49   12.556%   $66.9596   $66.96   $66.95   $67.00  
  Purchase #2 $45.78   8.597%   $49.7157   $49.72   $49.70   $49.70  
  Purchase #3 $54.95   3.784%   $57.0293   $57.03   $57.05   $57.00  
  Purchase #4 $45.60   9.733%   $50.0382   $50.04   $50.05   $50.00  
  Purchase #5 $12.66   6.441%   $13.4754   $13.48   $13.50   $13.50  
  Purchase #6 $204.98   8.681%   $222.7743   $222.77   $222.75   $222.80  
  Purchase #7 $226.71   5.774%   $239.8002   $239.80   $239.80   $239.80  
  7 purchase totals = $650.17       $699.7927   $699.80   $699.80   $699.80