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 $50.66   12.371%   $56.9271   $56.93   $56.95   $56.90  
  Purchase #2 $137.47   7.404%   $147.6483   $147.65   $147.65   $147.60  
  Purchase #3 $207.76   3.589%   $215.2165   $215.22   $215.20   $215.20  
  Purchase #4 $51.96   13.465%   $58.9564   $58.96   $58.95   $59.00  
  Purchase #5 $132.69   6.135%   $140.8305   $140.83   $140.85   $140.80  
  Purchase #6 $229.76   8.621%   $249.5676   $249.57   $249.55   $249.60  
  Purchase #7 $233.27   3.660%   $241.8077   $241.81   $241.80   $241.80  
  7 purchase totals = $1,043.57       $1,110.9541   $1,110.97   $1,110.95   $1,110.90