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 $72.81   12.833%   $82.1537   $82.15   $82.15   $82.20  
  Purchase #2 $236.44   8.655%   $256.9039   $256.90   $256.90   $256.90  
  Purchase #3 $164.70   7.760%   $177.4807   $177.48   $177.50   $177.50  
  Purchase #4 $79.38   10.372%   $87.6133   $87.61   $87.60   $87.60  
  Purchase #5 $182.36   13.477%   $206.9367   $206.94   $206.95   $206.90  
  Purchase #6 $32.54   5.600%   $34.3622   $34.36   $34.35   $34.40  
  Purchase #7 $165.37   7.708%   $178.1167   $178.12   $178.10   $178.10  
  7 purchase totals = $933.60       $1,023.5672   $1,023.56   $1,023.55   $1,023.60