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 $226.40   11.584%   $252.6262   $252.63   $252.65   $252.60  
  Purchase #2 $196.45   10.314%   $216.7119   $216.71   $216.70   $216.70  
  Purchase #3 $117.83   4.189%   $122.7659   $122.77   $122.75   $122.80  
  Purchase #4 $162.47   6.792%   $173.505   $173.51   $173.50   $173.50  
  Purchase #5 $31.43   10.401%   $34.699   $34.70   $34.70   $34.70  
  Purchase #6 $145.25   12.241%   $163.0301   $163.03   $163.05   $163.00  
  Purchase #7 $79.74   8.550%   $86.5578   $86.56   $86.55   $86.60  
  7 purchase totals = $959.57       $1,049.8959   $1,049.91   $1,049.90   $1,049.90