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 $226.96   6.846%   $242.4977   $242.50   $242.50   $242.50  
  Purchase #2 $181.77   12.792%   $205.022   $205.02   $205.00   $205.00  
  Purchase #3 $46.91   5.302%   $49.3972   $49.40   $49.40   $49.40  
  Purchase #4 $234.97   11.509%   $262.0127   $262.01   $262.00   $262.00  
  Purchase #5 $30.41   11.141%   $33.798   $33.80   $33.80   $33.80  
  Purchase #6 $5.39   12.332%   $6.0547   $6.05   $6.05   $6.10  
  Purchase #7 $168.42   10.850%   $186.6936   $186.69   $186.70   $186.70  
  7 purchase totals = $894.83       $985.4759   $985.47   $985.45   $985.50