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 $84.96   13.576%   $96.4942   $96.49   $96.50   $96.50  
  Purchase #2 $201.57   12.442%   $226.6493   $226.65   $226.65   $226.60  
  Purchase #3 $185.45   13.728%   $210.9086   $210.91   $210.90   $210.90  
  Purchase #4 $249.63   5.855%   $264.2458   $264.25   $264.25   $264.20  
  Purchase #5 $92.72   11.662%   $103.533   $103.53   $103.55   $103.50  
  Purchase #6 $193.68   10.116%   $213.2727   $213.27   $213.25   $213.30  
  Purchase #7 $228.82   4.705%   $239.586   $239.59   $239.60   $239.60  
  7 purchase totals = $1,236.83       $1,354.6896   $1,354.69   $1,354.70   $1,354.60