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 $207.51   6.291%   $220.5645   $220.56   $220.55   $220.60  
  Purchase #2 $172.79   7.439%   $185.6438   $185.64   $185.65   $185.60  
  Purchase #3 $126.83   7.383%   $136.1939   $136.19   $136.20   $136.20  
  Purchase #4 $39.36   8.313%   $42.632   $42.63   $42.65   $42.60  
  Purchase #5 $247.62   3.554%   $256.4204   $256.42   $256.40   $256.40  
  Purchase #6 $198.91   11.287%   $221.361   $221.36   $221.35   $221.40  
  Purchase #7 $55.93   9.689%   $61.3491   $61.35   $61.35   $61.30  
  7 purchase totals = $1,048.95       $1,124.1647   $1,124.15   $1,124.15   $1,124.10