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 $228.53   10.637%   $252.8387   $252.84   $252.85   $252.80  
  Purchase #2 $34.83   12.698%   $39.2527   $39.25   $39.25   $39.30  
  Purchase #3 $147.95   5.604%   $156.2411   $156.24   $156.25   $156.20  
  Purchase #4 $53.43   4.482%   $55.8247   $55.82   $55.80   $55.80  
  Purchase #5 $116.95   8.366%   $126.734   $126.73   $126.75   $126.70  
  Purchase #6 $17.45   12.741%   $19.6733   $19.67   $19.65   $19.70  
  Purchase #7 $56.49   7.379%   $60.6584   $60.66   $60.65   $60.70  
  7 purchase totals = $655.63       $711.2229   $711.21   $711.20   $711.20