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 $184.78   4.282%   $192.6923   $192.69   $192.70   $192.70  
  Purchase #2 $32.67   5.815%   $34.5698   $34.57   $34.55   $34.60  
  Purchase #3 $219.41   3.440%   $226.9577   $226.96   $226.95   $227.00  
  Purchase #4 $97.46   5.683%   $102.9987   $103.00   $103.00   $103.00  
  Purchase #5 $186.90   10.631%   $206.7693   $206.77   $206.75   $206.80  
  Purchase #6 $163.68   11.226%   $182.0547   $182.05   $182.05   $182.10  
  Purchase #7 $14.26   4.856%   $14.9525   $14.95   $14.95   $15.00  
  7 purchase totals = $899.16       $960.9950   $960.99   $960.95   $961.20