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 $124.86   9.691%   $136.9602   $136.96   $136.95   $137.00  
  Purchase #2 $126.26   13.130%   $142.8379   $142.84   $142.85   $142.80  
  Purchase #3 $151.54   5.748%   $160.2505   $160.25   $160.25   $160.30  
  Purchase #4 $103.83   4.126%   $108.114   $108.11   $108.10   $108.10  
  Purchase #5 $26.80   13.464%   $30.4084   $30.41   $30.40   $30.40  
  Purchase #6 $134.96   13.296%   $152.9043   $152.90   $152.90   $152.90  
  Purchase #7 $40.59   9.289%   $44.3604   $44.36   $44.35   $44.40  
  7 purchase totals = $708.84       $775.8357   $775.83   $775.80   $775.90