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 $53.77   4.346%   $56.1068   $56.11   $56.10   $56.10  
  Purchase #2 $221.67   10.425%   $244.7791   $244.78   $244.80   $244.80  
  Purchase #3 $55.59   13.566%   $63.1313   $63.13   $63.15   $63.10  
  Purchase #4 $59.66   6.704%   $63.6596   $63.66   $63.65   $63.70  
  Purchase #5 $178.66   6.387%   $190.071   $190.07   $190.05   $190.10  
  Purchase #6 $207.70   12.853%   $234.3957   $234.40   $234.40   $234.40  
  Purchase #7 $82.76   7.546%   $89.0051   $89.01   $89.00   $89.00  
  7 purchase totals = $859.81       $941.1486   $941.16   $941.15   $941.20