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 $24.95   8.450%   $27.0583   $27.06   $27.05   $27.10  
  Purchase #2 $196.98   4.832%   $206.4981   $206.50   $206.50   $206.50  
  Purchase #3 $163.51   6.745%   $174.5387   $174.54   $174.55   $174.50  
  Purchase #4 $153.86   8.409%   $166.7981   $166.80   $166.80   $166.80  
  Purchase #5 $84.69   13.479%   $96.1054   $96.11   $96.10   $96.10  
  Purchase #6 $112.91   3.425%   $116.7772   $116.78   $116.80   $116.80  
  Purchase #7 $196.64   7.856%   $212.088   $212.09   $212.10   $212.10  
  7 purchase totals = $933.54       $999.8638   $999.88   $999.90   $999.90