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 $22.46   4.829%   $23.5446   $23.54   $23.55   $23.50  
  Purchase #2 $48.87   9.706%   $53.6133   $53.61   $53.60   $53.60  
  Purchase #3 $168.90   7.592%   $181.7229   $181.72   $181.70   $181.70  
  Purchase #4 $5.30   12.494%   $5.9622   $5.96   $5.95   $6.00  
  Purchase #5 $96.70   13.119%   $109.3861   $109.39   $109.40   $109.40  
  Purchase #6 $224.73   9.201%   $245.4074   $245.41   $245.40   $245.40  
  Purchase #7 $126.44   10.617%   $139.8641   $139.86   $139.85   $139.90  
  7 purchase totals = $693.40       $759.5006   $759.49   $759.45   $759.50