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 $85.51   9.474%   $93.6112   $93.61   $93.60   $93.60  
  Purchase #2 $248.42   4.239%   $258.9505   $258.95   $258.95   $259.00  
  Purchase #3 $100.50   13.650%   $114.2183   $114.22   $114.20   $114.20  
  Purchase #4 $220.75   4.510%   $230.7058   $230.71   $230.70   $230.70  
  Purchase #5 $163.47   12.378%   $183.7043   $183.70   $183.70   $183.70  
  Purchase #6 $65.98   13.721%   $75.0331   $75.03   $75.05   $75.00  
  Purchase #7 $196.67   5.681%   $207.8428   $207.84   $207.85   $207.80  
  7 purchase totals = $1,081.30       $1,164.0660   $1,164.06   $1,164.05   $1,164.00