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 $23.45   9.802%   $25.7486   $25.75   $25.75   $25.70  
  Purchase #2 $230.61   4.318%   $240.5677   $240.57   $240.55   $240.60  
  Purchase #3 $191.53   9.446%   $209.6219   $209.62   $209.60   $209.60  
  Purchase #4 $136.67   5.699%   $144.4588   $144.46   $144.45   $144.50  
  Purchase #5 $226.72   6.426%   $241.289   $241.29   $241.30   $241.30  
  Purchase #6 $161.79   13.617%   $183.8209   $183.82   $183.80   $183.80  
  Purchase #7 $104.59   13.598%   $118.8121   $118.81   $118.80   $118.80  
  7 purchase totals = $1,075.36       $1,164.3190   $1,164.32   $1,164.25   $1,164.30