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 $205.85   12.859%   $232.3203   $232.32   $232.30   $232.30  
  Purchase #2 $120.34   11.190%   $133.806   $133.81   $133.80   $133.80  
  Purchase #3 $47.64   3.379%   $49.2498   $49.25   $49.25   $49.20  
  Purchase #4 $41.90   4.786%   $43.9053   $43.91   $43.90   $43.90  
  Purchase #5 $191.35   5.528%   $201.9278   $201.93   $201.95   $201.90  
  Purchase #6 $147.25   7.425%   $158.1833   $158.18   $158.20   $158.20  
  Purchase #7 $247.77   5.434%   $261.2338   $261.23   $261.25   $261.20  
  7 purchase totals = $1,002.10       $1,080.6263   $1,080.63   $1,080.65   $1,080.50