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 $225.71   10.744%   $249.9603   $249.96   $249.95   $250.00  
  Purchase #2 $222.91   10.205%   $245.658   $245.66   $245.65   $245.70  
  Purchase #3 $186.67   3.870%   $193.8941   $193.89   $193.90   $193.90  
  Purchase #4 $92.52   12.460%   $104.048   $104.05   $104.05   $104.00  
  Purchase #5 $138.38   6.293%   $147.0883   $147.09   $147.10   $147.10  
  Purchase #6 $217.34   8.831%   $236.5333   $236.53   $236.55   $236.50  
  Purchase #7 $177.78   7.224%   $190.6228   $190.62   $190.60   $190.60  
  7 purchase totals = $1,261.31       $1,367.8048   $1,367.80   $1,367.80   $1,367.80