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 $241.79   12.595%   $272.2435   $272.24   $272.25   $272.20  
  Purchase #2 $215.51   9.354%   $235.6688   $235.67   $235.65   $235.70  
  Purchase #3 $102.39   4.359%   $106.8532   $106.85   $106.85   $106.90  
  Purchase #4 $223.35   11.773%   $249.645   $249.65   $249.65   $249.60  
  Purchase #5 $119.56   3.468%   $123.7063   $123.71   $123.70   $123.70  
  Purchase #6 $50.81   11.110%   $56.455   $56.46   $56.45   $56.50  
  Purchase #7 $209.93   8.601%   $227.9861   $227.99   $228.00   $228.00  
  7 purchase totals = $1,163.34       $1,272.5579   $1,272.57   $1,272.55   $1,272.60