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 $59.60   6.125%   $63.2505   $63.25   $63.25   $63.30  
  Purchase #2 $79.35   6.161%   $84.2388   $84.24   $84.25   $84.20  
  Purchase #3 $140.67   6.424%   $149.7066   $149.71   $149.70   $149.70  
  Purchase #4 $249.67   7.537%   $268.4876   $268.49   $268.50   $268.50  
  Purchase #5 $53.69   3.344%   $55.4854   $55.49   $55.50   $55.50  
  Purchase #6 $98.45   8.230%   $106.5524   $106.55   $106.55   $106.60  
  Purchase #7 $64.84   7.848%   $69.9286   $69.93   $69.95   $69.90  
  7 purchase totals = $746.27       $797.6499   $797.66   $797.70   $797.70