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 $73.63   13.501%   $83.5708   $83.57   $83.55   $83.60  
  Purchase #2 $122.34   3.678%   $126.8397   $126.84   $126.85   $126.80  
  Purchase #3 $228.60   10.873%   $253.4557   $253.46   $253.45   $253.50  
  Purchase #4 $153.39   8.468%   $166.3791   $166.38   $166.40   $166.40  
  Purchase #5 $150.69   8.347%   $163.2681   $163.27   $163.25   $163.30  
  Purchase #6 $182.40   3.162%   $188.1675   $188.17   $188.15   $188.20  
  Purchase #7 $39.84   7.818%   $42.9547   $42.95   $42.95   $43.00  
  7 purchase totals = $950.89       $1,024.6356   $1,024.64   $1,024.60   $1,024.80