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 $38.92   6.147%   $41.3124   $41.31   $41.30   $41.30  
  Purchase #2 $142.27   12.708%   $160.3497   $160.35   $160.35   $160.30  
  Purchase #3 $65.90   11.223%   $73.296   $73.30   $73.30   $73.30  
  Purchase #4 $101.71   10.794%   $112.6886   $112.69   $112.70   $112.70  
  Purchase #5 $181.88   10.623%   $201.2011   $201.20   $201.20   $201.20  
  Purchase #6 $127.32   11.560%   $142.0382   $142.04   $142.05   $142.00  
  Purchase #7 $164.44   6.138%   $174.5333   $174.53   $174.55   $174.50  
  7 purchase totals = $822.44       $905.4193   $905.42   $905.45   $905.30