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 $186.96   11.619%   $208.6829   $208.68   $208.70   $208.70  
  Purchase #2 $82.67   5.135%   $86.9151   $86.92   $86.90   $86.90  
  Purchase #3 $245.85   5.744%   $259.9716   $259.97   $259.95   $260.00  
  Purchase #4 $232.85   13.362%   $263.9634   $263.96   $263.95   $264.00  
  Purchase #5 $108.67   13.200%   $123.0144   $123.01   $123.00   $123.00  
  Purchase #6 $5.97   11.262%   $6.6423   $6.64   $6.65   $6.60  
  Purchase #7 $151.61   4.373%   $158.2399   $158.24   $158.25   $158.20  
  7 purchase totals = $1,014.58       $1,107.4296   $1,107.42   $1,107.40   $1,107.40