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 $23.30   13.323%   $26.4043   $26.40   $26.40   $26.40  
  Purchase #2 $157.76   8.577%   $171.2911   $171.29   $171.30   $171.30  
  Purchase #3 $63.91   9.373%   $69.9003   $69.90   $69.90   $69.90  
  Purchase #4 $52.35   12.727%   $59.0126   $59.01   $59.00   $59.00  
  Purchase #5 $125.97   8.722%   $136.9571   $136.96   $136.95   $137.00  
  Purchase #6 $38.64   6.767%   $41.2548   $41.25   $41.25   $41.30  
  Purchase #7 $86.96   8.267%   $94.149   $94.15   $94.15   $94.10  
  7 purchase totals = $548.89       $598.9692   $598.96   $598.95   $599.00