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 $38.32   8.273%   $41.4902   $41.49   $41.50   $41.50  
  Purchase #2 $171.37   11.292%   $190.7211   $190.72   $190.70   $190.70  
  Purchase #3 $212.29   3.679%   $220.1001   $220.10   $220.10   $220.10  
  Purchase #4 $10.71   7.626%   $11.5267   $11.53   $11.55   $11.50  
  Purchase #5 $92.80   4.786%   $97.2414   $97.24   $97.25   $97.20  
  Purchase #6 $146.66   8.688%   $159.4018   $159.40   $159.40   $159.40  
  Purchase #7 $38.86   7.602%   $41.8141   $41.81   $41.80   $41.80  
  7 purchase totals = $711.01       $762.2954   $762.29   $762.30   $762.20