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 $61.69   6.272%   $65.5592   $65.56   $65.55   $65.60  
  Purchase #2 $198.82   8.688%   $216.0935   $216.09   $216.10   $216.10  
  Purchase #3 $84.54   9.608%   $92.6626   $92.66   $92.65   $92.70  
  Purchase #4 $171.97   10.872%   $190.6666   $190.67   $190.65   $190.70  
  Purchase #5 $80.55   5.311%   $84.828   $84.83   $84.85   $84.80  
  Purchase #6 $185.72   12.484%   $208.9053   $208.91   $208.90   $208.90  
  Purchase #7 $132.26   4.705%   $138.4828   $138.48   $138.50   $138.50  
  7 purchase totals = $915.55       $997.1980   $997.20   $997.20   $997.30