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 $164.54   11.670%   $183.7418   $183.74   $183.75   $183.70  
  Purchase #2 $81.78   13.232%   $92.6011   $92.60   $92.60   $92.60  
  Purchase #3 $154.66   8.462%   $167.7473   $167.75   $167.75   $167.70  
  Purchase #4 $13.38   11.640%   $14.9374   $14.94   $14.95   $14.90  
  Purchase #5 $31.60   6.472%   $33.6452   $33.65   $33.65   $33.60  
  Purchase #6 $67.73   4.233%   $70.597   $70.60   $70.60   $70.60  
  Purchase #7 $186.86   11.275%   $207.9285   $207.93   $207.95   $207.90  
  7 purchase totals = $700.55       $771.1983   $771.21   $771.25   $771.00