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 $59.27   3.172%   $61.15   $61.15   $61.15   $61.20  
  Purchase #2 $213.72   12.182%   $239.7554   $239.76   $239.75   $239.80  
  Purchase #3 $160.61   4.371%   $167.6303   $167.63   $167.65   $167.60  
  Purchase #4 $63.47   11.140%   $70.5406   $70.54   $70.55   $70.50  
  Purchase #5 $81.60   8.513%   $88.5466   $88.55   $88.55   $88.50  
  Purchase #6 $249.31   11.534%   $278.0654   $278.07   $278.05   $278.10  
  Purchase #7 $69.29   11.117%   $76.993   $76.99   $77.00   $77.00  
  7 purchase totals = $897.27       $982.6813   $982.69   $982.70   $982.70