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 $46.77   5.512%   $49.348   $49.35   $49.35   $49.30  
  Purchase #2 $164.86   12.158%   $184.9037   $184.90   $184.90   $184.90  
  Purchase #3 $106.76   6.510%   $113.7101   $113.71   $113.70   $113.70  
  Purchase #4 $190.27   8.315%   $206.091   $206.09   $206.10   $206.10  
  Purchase #5 $38.96   11.301%   $43.3629   $43.36   $43.35   $43.40  
  Purchase #6 $64.78   8.300%   $70.1567   $70.16   $70.15   $70.20  
  Purchase #7 $73.84   4.398%   $77.0875   $77.09   $77.10   $77.10  
  7 purchase totals = $686.24       $744.6599   $744.66   $744.65   $744.70