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 $93.36   10.608%   $103.2636   $103.26   $103.25   $103.30  
  Purchase #2 $28.81   8.138%   $31.1546   $31.15   $31.15   $31.20  
  Purchase #3 $61.37   6.362%   $65.2744   $65.27   $65.25   $65.30  
  Purchase #4 $180.42   7.198%   $193.4066   $193.41   $193.40   $193.40  
  Purchase #5 $185.68   6.710%   $198.1391   $198.14   $198.15   $198.10  
  Purchase #6 $109.80   5.163%   $115.469   $115.47   $115.45   $115.50  
  Purchase #7 $89.90   3.233%   $92.8065   $92.81   $92.80   $92.80  
  7 purchase totals = $749.34       $799.5138   $799.51   $799.45   $799.60