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 $228.26   5.667%   $241.1955   $241.20   $241.20   $241.20  
  Purchase #2 $23.74   3.119%   $24.4805   $24.48   $24.50   $24.50  
  Purchase #3 $227.85   6.204%   $241.9858   $241.99   $242.00   $242.00  
  Purchase #4 $25.60   10.845%   $28.3763   $28.38   $28.40   $28.40  
  Purchase #5 $136.55   3.483%   $141.306   $141.31   $141.30   $141.30  
  Purchase #6 $250.29   11.655%   $279.4613   $279.46   $279.45   $279.50  
  Purchase #7 $190.96   5.680%   $201.8065   $201.81   $201.80   $201.80  
  7 purchase totals = $1,083.25       $1,158.6119   $1,158.63   $1,158.65   $1,158.70