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 $49.92   3.590%   $51.7121   $51.71   $51.70   $51.70  
  Purchase #2 $220.65   6.293%   $234.5355   $234.54   $234.55   $234.50  
  Purchase #3 $249.31   13.812%   $283.7447   $283.74   $283.75   $283.70  
  Purchase #4 $196.69   9.184%   $214.754   $214.75   $214.75   $214.80  
  Purchase #5 $106.63   8.672%   $115.877   $115.88   $115.90   $115.90  
  Purchase #6 $133.83   9.696%   $146.8062   $146.81   $146.80   $146.80  
  Purchase #7 $213.62   9.818%   $234.5932   $234.59   $234.60   $234.60  
  7 purchase totals = $1,170.65       $1,282.0227   $1,282.02   $1,282.05   $1,282.00