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 $208.31   12.543%   $234.4383   $234.44   $234.45   $234.40  
  Purchase #2 $124.91   7.462%   $134.2308   $134.23   $134.25   $134.20  
  Purchase #3 $9.81   4.405%   $10.2421   $10.24   $10.25   $10.20  
  Purchase #4 $237.85   6.147%   $252.4706   $252.47   $252.45   $252.50  
  Purchase #5 $131.45   12.833%   $148.319   $148.32   $148.30   $148.30  
  Purchase #6 $58.71   4.773%   $61.5122   $61.51   $61.50   $61.50  
  Purchase #7 $186.95   5.393%   $197.0322   $197.03   $197.05   $197.00  
  7 purchase totals = $957.99       $1,038.2452   $1,038.24   $1,038.25   $1,038.10