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 $64.61   7.698%   $69.5837   $69.58   $69.60   $69.60  
  Purchase #2 $34.91   12.362%   $39.2256   $39.23   $39.25   $39.20  
  Purchase #3 $105.47   8.647%   $114.59   $114.59   $114.60   $114.60  
  Purchase #4 $33.87   6.320%   $36.0106   $36.01   $36.00   $36.00  
  Purchase #5 $57.73   6.156%   $61.2839   $61.28   $61.30   $61.30  
  Purchase #6 $164.57   8.455%   $178.4844   $178.48   $178.50   $178.50  
  Purchase #7 $119.64   12.714%   $134.851   $134.85   $134.85   $134.90  
  7 purchase totals = $580.80       $634.0292   $634.02   $634.10   $634.10