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 $34.25   12.264%   $38.4504   $38.45   $38.45   $38.50  
  Purchase #2 $135.91   11.509%   $151.5519   $151.55   $151.55   $151.60  
  Purchase #3 $239.40   13.209%   $271.0223   $271.02   $271.00   $271.00  
  Purchase #4 $232.29   7.486%   $249.6792   $249.68   $249.70   $249.70  
  Purchase #5 $101.69   6.437%   $108.2358   $108.24   $108.25   $108.20  
  Purchase #6 $152.25   5.747%   $160.9998   $161.00   $161.00   $161.00  
  Purchase #7 $160.64   9.569%   $176.0116   $176.01   $176.00   $176.00  
  7 purchase totals = $1,056.43       $1,155.9510   $1,155.95   $1,155.95   $1,156.00