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 $93.81   3.141%   $96.7566   $96.76   $96.75   $96.80  
  Purchase #2 $49.99   13.351%   $56.6642   $56.66   $56.65   $56.70  
  Purchase #3 $175.82   5.657%   $185.7661   $185.77   $185.75   $185.80  
  Purchase #4 $43.43   13.466%   $49.2783   $49.28   $49.30   $49.30  
  Purchase #5 $126.67   10.127%   $139.4979   $139.50   $139.50   $139.50  
  Purchase #6 $187.84   13.247%   $212.7232   $212.72   $212.70   $212.70  
  Purchase #7 $8.28   3.752%   $8.5907   $8.59   $8.60   $8.60  
  7 purchase totals = $685.84       $749.2770   $749.28   $749.25   $749.40