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 $112.32   12.442%   $126.2949   $126.29   $126.30   $126.30  
  Purchase #2 $228.51   5.277%   $240.5685   $240.57   $240.55   $240.60  
  Purchase #3 $187.81   7.615%   $202.1117   $202.11   $202.10   $202.10  
  Purchase #4 $127.75   11.354%   $142.2547   $142.25   $142.25   $142.30  
  Purchase #5 $114.61   4.233%   $119.4614   $119.46   $119.45   $119.50  
  Purchase #6 $44.66   9.227%   $48.7808   $48.78   $48.80   $48.80  
  Purchase #7 $158.40   10.447%   $174.948   $174.95   $174.95   $174.90  
  7 purchase totals = $974.06       $1,054.4200   $1,054.41   $1,054.40   $1,054.50