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 $226.67   10.268%   $249.9445   $249.94   $249.95   $249.90  
  Purchase #2 $206.53   13.719%   $234.8639   $234.86   $234.85   $234.90  
  Purchase #3 $85.40   6.129%   $90.6342   $90.63   $90.65   $90.60  
  Purchase #4 $201.94   12.576%   $227.336   $227.34   $227.35   $227.30  
  Purchase #5 $229.45   12.228%   $257.5071   $257.51   $257.50   $257.50  
  Purchase #6 $93.76   8.144%   $101.3958   $101.40   $101.40   $101.40  
  Purchase #7 $237.58   4.475%   $248.2117   $248.21   $248.20   $248.20  
  7 purchase totals = $1,281.33       $1,409.8932   $1,409.89   $1,409.90   $1,409.80