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 $227.68   10.127%   $250.7372   $250.74   $250.75   $250.70  
  Purchase #2 $199.81   6.245%   $212.2881   $212.29   $212.30   $212.30  
  Purchase #3 $79.31   4.269%   $82.6957   $82.70   $82.70   $82.70  
  Purchase #4 $96.31   13.533%   $109.3436   $109.34   $109.35   $109.30  
  Purchase #5 $201.49   6.186%   $213.9542   $213.95   $213.95   $214.00  
  Purchase #6 $26.92   6.266%   $28.6068   $28.61   $28.60   $28.60  
  Purchase #7 $45.53   3.834%   $47.2756   $47.28   $47.30   $47.30  
  7 purchase totals = $877.05       $944.9012   $944.91   $944.95   $944.90