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 $211.76   13.811%   $241.0062   $241.01   $241.00   $241.00  
  Purchase #2 $69.71   6.351%   $74.1373   $74.14   $74.15   $74.10  
  Purchase #3 $28.70   5.410%   $30.2527   $30.25   $30.25   $30.30  
  Purchase #4 $43.56   5.686%   $46.0368   $46.04   $46.05   $46.00  
  Purchase #5 $153.48   11.770%   $171.5446   $171.54   $171.55   $171.50  
  Purchase #6 $135.65   13.787%   $154.3521   $154.35   $154.35   $154.40  
  Purchase #7 $34.58   7.509%   $37.1766   $37.18   $37.20   $37.20  
  7 purchase totals = $677.44       $754.5063   $754.51   $754.55   $754.50