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 $85.90   12.466%   $96.6083   $96.61   $96.60   $96.60  
  Purchase #2 $125.29   5.207%   $131.8139   $131.81   $131.80   $131.80  
  Purchase #3 $77.27   7.794%   $83.2924   $83.29   $83.30   $83.30  
  Purchase #4 $49.75   4.702%   $52.0892   $52.09   $52.10   $52.10  
  Purchase #5 $110.89   13.222%   $125.5519   $125.55   $125.55   $125.60  
  Purchase #6 $214.28   13.397%   $242.9871   $242.99   $243.00   $243.00  
  Purchase #7 $50.49   12.182%   $56.6407   $56.64   $56.65   $56.60  
  7 purchase totals = $713.87       $788.9835   $788.98   $789.00   $789.00