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 $241.61   3.433%   $249.9045   $249.90   $249.90   $249.90  
  Purchase #2 $157.95   12.435%   $177.5911   $177.59   $177.60   $177.60  
  Purchase #3 $184.75   9.731%   $202.728   $202.73   $202.75   $202.70  
  Purchase #4 $166.25   4.670%   $174.0139   $174.01   $174.00   $174.00  
  Purchase #5 $225.54   4.250%   $235.1255   $235.13   $235.15   $235.10  
  Purchase #6 $51.74   13.385%   $58.6654   $58.67   $58.65   $58.70  
  Purchase #7 $229.78   13.835%   $261.5701   $261.57   $261.55   $261.60  
  7 purchase totals = $1,257.62       $1,359.5985   $1,359.60   $1,359.60   $1,359.60