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 $63.68   6.182%   $67.6167   $67.62   $67.60   $67.60  
  Purchase #2 $86.58   10.263%   $95.4657   $95.47   $95.45   $95.50  
  Purchase #3 $248.49   5.119%   $261.2102   $261.21   $261.20   $261.20  
  Purchase #4 $228.27   9.855%   $250.766   $250.77   $250.75   $250.80  
  Purchase #5 $79.53   8.116%   $85.9847   $85.98   $86.00   $86.00  
  Purchase #6 $13.85   6.518%   $14.7527   $14.75   $14.75   $14.80  
  Purchase #7 $187.97   9.487%   $205.8027   $205.80   $205.80   $205.80  
  7 purchase totals = $908.37       $981.5987   $981.60   $981.55   $981.70