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 $216.32   11.530%   $241.2617   $241.26   $241.25   $241.30  
  Purchase #2 $215.87   6.776%   $230.4974   $230.50   $230.50   $230.50  
  Purchase #3 $114.43   9.804%   $125.6487   $125.65   $125.65   $125.60  
  Purchase #4 $56.55   13.557%   $64.2165   $64.22   $64.20   $64.20  
  Purchase #5 $239.53   10.371%   $264.3717   $264.37   $264.35   $264.40  
  Purchase #6 $194.83   6.775%   $208.0297   $208.03   $208.05   $208.00  
  Purchase #7 $211.28   8.188%   $228.5796   $228.58   $228.60   $228.60  
  7 purchase totals = $1,248.81       $1,362.6053   $1,362.61   $1,362.60   $1,362.60