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 $168.85   13.796%   $192.1445   $192.14   $192.15   $192.10  
  Purchase #2 $203.66   11.246%   $226.5636   $226.56   $226.55   $226.60  
  Purchase #3 $35.62   9.116%   $38.8671   $38.87   $38.85   $38.90  
  Purchase #4 $119.83   3.653%   $124.2074   $124.21   $124.20   $124.20  
  Purchase #5 $153.72   7.138%   $164.6925   $164.69   $164.70   $164.70  
  Purchase #6 $62.27   9.620%   $68.2604   $68.26   $68.25   $68.30  
  Purchase #7 $215.50   8.839%   $234.548   $234.55   $234.55   $234.50  
  7 purchase totals = $959.45       $1,049.2835   $1,049.28   $1,049.25   $1,049.30