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 $14.60   13.311%   $16.5434   $16.54   $16.55   $16.50  
  Purchase #2 $174.68   10.752%   $193.4616   $193.46   $193.45   $193.50  
  Purchase #3 $50.61   3.738%   $52.5018   $52.50   $52.50   $52.50  
  Purchase #4 $162.65   7.203%   $174.3657   $174.37   $174.35   $174.40  
  Purchase #5 $155.72   11.686%   $173.9174   $173.92   $173.90   $173.90  
  Purchase #6 $32.82   5.629%   $34.6674   $34.67   $34.65   $34.70  
  Purchase #7 $248.62   4.282%   $259.2659   $259.27   $259.25   $259.30  
  7 purchase totals = $839.70       $904.7232   $904.73   $904.65   $904.80