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 $119.60   11.578%   $133.4473   $133.45   $133.45   $133.40  
  Purchase #2 $32.88   12.209%   $36.8943   $36.89   $36.90   $36.90  
  Purchase #3 $107.48   6.603%   $114.5769   $114.58   $114.60   $114.60  
  Purchase #4 $215.88   3.620%   $223.6949   $223.69   $223.70   $223.70  
  Purchase #5 $167.81   5.266%   $176.6469   $176.65   $176.65   $176.60  
  Purchase #6 $210.76   10.643%   $233.1912   $233.19   $233.20   $233.20  
  Purchase #7 $104.68   3.437%   $108.2779   $108.28   $108.30   $108.30  
  7 purchase totals = $959.09       $1,026.7294   $1,026.73   $1,026.80   $1,026.70