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 $53.62   5.774%   $56.716   $56.72   $56.70   $56.70  
  Purchase #2 $195.79   3.497%   $202.6368   $202.64   $202.65   $202.60  
  Purchase #3 $65.49   5.687%   $69.2144   $69.21   $69.20   $69.20  
  Purchase #4 $30.79   3.305%   $31.8076   $31.81   $31.80   $31.80  
  Purchase #5 $11.30   8.868%   $12.3021   $12.30   $12.30   $12.30  
  Purchase #6 $74.48   3.810%   $77.3177   $77.32   $77.30   $77.30  
  Purchase #7 $192.61   11.180%   $214.1438   $214.14   $214.15   $214.10  
  7 purchase totals = $624.08       $664.1384   $664.14   $664.10   $664.00