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 $28.96   13.811%   $32.9597   $32.96   $32.95   $33.00  
  Purchase #2 $186.41   8.832%   $202.8737   $202.87   $202.85   $202.90  
  Purchase #3 $151.92   4.835%   $159.2653   $159.27   $159.25   $159.30  
  Purchase #4 $58.44   8.633%   $63.4851   $63.49   $63.50   $63.50  
  Purchase #5 $161.47   6.436%   $171.8622   $171.86   $171.85   $171.90  
  Purchase #6 $187.26   10.478%   $206.8811   $206.88   $206.90   $206.90  
  Purchase #7 $53.60   12.315%   $60.2008   $60.20   $60.20   $60.20  
  7 purchase totals = $828.06       $897.5279   $897.53   $897.50   $897.70