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 $52.69   6.130%   $55.9199   $55.92   $55.90   $55.90  
  Purchase #2 $196.93   10.661%   $217.9247   $217.92   $217.90   $217.90  
  Purchase #3 $231.55   9.109%   $252.6419   $252.64   $252.65   $252.60  
  Purchase #4 $64.65   3.726%   $67.0589   $67.06   $67.05   $67.10  
  Purchase #5 $156.26   3.331%   $161.465   $161.47   $161.45   $161.50  
  Purchase #6 $21.44   8.702%   $23.3057   $23.31   $23.30   $23.30  
  Purchase #7 $123.27   8.866%   $134.1991   $134.20   $134.20   $134.20  
  7 purchase totals = $846.79       $912.5152   $912.52   $912.45   $912.50