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 $248.88   5.266%   $261.986   $261.99   $262.00   $262.00  
  Purchase #2 $25.96   10.826%   $28.7704   $28.77   $28.75   $28.80  
  Purchase #3 $15.57   3.228%   $16.0726   $16.07   $16.05   $16.10  
  Purchase #4 $128.56   11.315%   $143.1066   $143.11   $143.10   $143.10  
  Purchase #5 $201.43   4.725%   $210.9476   $210.95   $210.95   $210.90  
  Purchase #6 $113.48   6.608%   $120.9788   $120.98   $121.00   $121.00  
  Purchase #7 $230.49   8.852%   $250.893   $250.89   $250.90   $250.90  
  7 purchase totals = $964.37       $1,032.7550   $1,032.76   $1,032.75   $1,032.80