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 $70.53   4.509%   $73.7102   $73.71   $73.70   $73.70  
  Purchase #2 $106.64   5.743%   $112.7643   $112.76   $112.75   $112.80  
  Purchase #3 $90.70   3.645%   $94.006   $94.01   $94.00   $94.00  
  Purchase #4 $86.97   9.263%   $95.026   $95.03   $95.05   $95.00  
  Purchase #5 $73.88   3.820%   $76.7022   $76.70   $76.70   $76.70  
  Purchase #6 $226.25   3.575%   $234.3384   $234.34   $234.35   $234.30  
  Purchase #7 $36.69   4.583%   $38.3715   $38.37   $38.35   $38.40  
  7 purchase totals = $691.66       $724.9186   $724.92   $724.90   $724.90