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 $158.99   3.277%   $164.2001   $164.20   $164.20   $164.20  
  Purchase #2 $240.26   10.588%   $265.6987   $265.70   $265.70   $265.70  
  Purchase #3 $20.43   10.493%   $22.5737   $22.57   $22.55   $22.60  
  Purchase #4 $45.94   8.641%   $49.9097   $49.91   $49.90   $49.90  
  Purchase #5 $46.27   7.276%   $49.6366   $49.64   $49.65   $49.60  
  Purchase #6 $244.80   7.217%   $262.4672   $262.47   $262.45   $262.50  
  Purchase #7 $83.32   7.794%   $89.814   $89.81   $89.80   $89.80  
  7 purchase totals = $840.01       $904.3000   $904.30   $904.25   $904.30