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 $229.63   10.416%   $253.5483   $253.55   $253.55   $253.50  
  Purchase #2 $227.83   9.593%   $249.6857   $249.69   $249.70   $249.70  
  Purchase #3 $11.69   9.611%   $12.8135   $12.81   $12.80   $12.80  
  Purchase #4 $248.71   9.544%   $272.4469   $272.45   $272.45   $272.40  
  Purchase #5 $163.88   12.746%   $184.7681   $184.77   $184.75   $184.80  
  Purchase #6 $30.47   12.559%   $34.2967   $34.30   $34.30   $34.30  
  Purchase #7 $225.83   9.112%   $246.4076   $246.41   $246.40   $246.40  
  7 purchase totals = $1,138.04       $1,253.9668   $1,253.98   $1,253.95   $1,253.90