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 $113.55   11.860%   $127.017   $127.02   $127.00   $127.00  
  Purchase #2 $248.98   3.788%   $258.4114   $258.41   $258.40   $258.40  
  Purchase #3 $54.41   10.526%   $60.1372   $60.14   $60.15   $60.10  
  Purchase #4 $47.49   12.572%   $53.4604   $53.46   $53.45   $53.50  
  Purchase #5 $5.47   10.217%   $6.0289   $6.03   $6.05   $6.00  
  Purchase #6 $125.82   8.591%   $136.6292   $136.63   $136.65   $136.60  
  Purchase #7 $155.70   9.614%   $170.669   $170.67   $170.65   $170.70  
  7 purchase totals = $751.42       $812.3531   $812.36   $812.35   $812.30