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 $162.72   13.719%   $185.0436   $185.04   $185.05   $185.00  
  Purchase #2 $151.28   5.254%   $159.2283   $159.23   $159.25   $159.20  
  Purchase #3 $208.66   7.186%   $223.6543   $223.65   $223.65   $223.70  
  Purchase #4 $122.55   4.139%   $127.6223   $127.62   $127.60   $127.60  
  Purchase #5 $182.81   9.415%   $200.0216   $200.02   $200.00   $200.00  
  Purchase #6 $176.63   12.322%   $198.3943   $198.39   $198.40   $198.40  
  Purchase #7 $230.74   9.358%   $252.3326   $252.33   $252.35   $252.30  
  7 purchase totals = $1,235.39       $1,346.2970   $1,346.28   $1,346.30   $1,346.20