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 $148.27   13.805%   $168.7387   $168.74   $168.75   $168.70  
  Purchase #2 $94.57   12.785%   $106.6608   $106.66   $106.65   $106.70  
  Purchase #3 $76.66   8.845%   $83.4406   $83.44   $83.45   $83.40  
  Purchase #4 $159.60   11.274%   $177.5933   $177.59   $177.60   $177.60  
  Purchase #5 $13.39   13.730%   $15.2284   $15.23   $15.25   $15.20  
  Purchase #6 $109.77   3.552%   $113.669   $113.67   $113.65   $113.70  
  Purchase #7 $52.92   12.595%   $59.5853   $59.59   $59.60   $59.60  
  7 purchase totals = $655.18       $724.9161   $724.92   $724.95   $724.90