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   13.464%   $184.6286   $184.63   $184.65   $184.60  
  Purchase #2 $235.97   13.848%   $268.6471   $268.65   $268.65   $268.60  
  Purchase #3 $35.62   7.476%   $38.283   $38.28   $38.30   $38.30  
  Purchase #4 $185.74   3.592%   $192.4118   $192.41   $192.40   $192.40  
  Purchase #5 $238.91   3.705%   $247.7616   $247.76   $247.75   $247.80  
  Purchase #6 $205.88   3.688%   $213.4729   $213.47   $213.45   $213.50  
  Purchase #7 $139.30   5.577%   $147.0688   $147.07   $147.05   $147.10  
  7 purchase totals = $1,204.14       $1,292.2738   $1,292.27   $1,292.25   $1,292.30