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 $49.76   3.154%   $51.3294   $51.33   $51.35   $51.30  
  Purchase #2 $124.83   13.503%   $141.6858   $141.69   $141.70   $141.70  
  Purchase #3 $237.28   10.508%   $262.2134   $262.21   $262.20   $262.20  
  Purchase #4 $202.66   9.185%   $221.2743   $221.27   $221.25   $221.30  
  Purchase #5 $87.88   9.670%   $96.378   $96.38   $96.40   $96.40  
  Purchase #6 $123.53   13.277%   $139.9311   $139.93   $139.95   $139.90  
  Purchase #7 $173.69   5.496%   $183.236   $183.24   $183.25   $183.20  
  7 purchase totals = $999.63       $1,096.0480   $1,096.05   $1,096.10   $1,096.00