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 $161.28   13.821%   $183.5705   $183.57   $183.55   $183.60  
  Purchase #2 $239.40   3.545%   $247.8867   $247.89   $247.90   $247.90  
  Purchase #3 $72.38   11.818%   $80.9339   $80.93   $80.95   $80.90  
  Purchase #4 $190.76   8.646%   $207.2531   $207.25   $207.25   $207.30  
  Purchase #5 $101.95   3.459%   $105.4765   $105.48   $105.50   $105.50  
  Purchase #6 $171.93   8.145%   $185.9337   $185.93   $185.95   $185.90  
  Purchase #7 $212.30   8.440%   $230.2181   $230.22   $230.20   $230.20  
  7 purchase totals = $1,150.00       $1,241.2725   $1,241.27   $1,241.30   $1,241.30