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 $232.80   6.864%   $248.7794   $248.78   $248.80   $248.80  
  Purchase #2 $114.98   10.166%   $126.6689   $126.67   $126.65   $126.70  
  Purchase #3 $164.25   11.379%   $182.94   $182.94   $182.95   $182.90  
  Purchase #4 $208.53   6.141%   $221.3358   $221.34   $221.35   $221.30  
  Purchase #5 $40.42   12.325%   $45.4018   $45.40   $45.40   $45.40  
  Purchase #6 $130.48   9.582%   $142.9826   $142.98   $143.00   $143.00  
  Purchase #7 $220.46   13.384%   $249.9664   $249.97   $249.95   $250.00  
  7 purchase totals = $1,111.92       $1,218.0749   $1,218.08   $1,218.10   $1,218.10