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 $183.81   10.240%   $202.6321   $202.63   $202.65   $202.60  
  Purchase #2 $43.28   12.549%   $48.7112   $48.71   $48.70   $48.70  
  Purchase #3 $151.36   3.794%   $157.1026   $157.10   $157.10   $157.10  
  Purchase #4 $128.78   12.425%   $144.7809   $144.78   $144.80   $144.80  
  Purchase #5 $162.62   9.807%   $178.5681   $178.57   $178.55   $178.60  
  Purchase #6 $108.80   8.706%   $118.2721   $118.27   $118.25   $118.30  
  Purchase #7 $180.28   3.540%   $186.6619   $186.66   $186.65   $186.70  
  7 purchase totals = $958.93       $1,036.7289   $1,036.72   $1,036.70   $1,036.80