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 $53.43   13.327%   $60.5506   $60.55   $60.55   $60.60  
  Purchase #2 $131.53   12.218%   $147.6003   $147.60   $147.60   $147.60  
  Purchase #3 $168.77   9.381%   $184.6023   $184.60   $184.60   $184.60  
  Purchase #4 $155.74   13.435%   $176.6637   $176.66   $176.65   $176.70  
  Purchase #5 $17.68   8.387%   $19.1628   $19.16   $19.15   $19.20  
  Purchase #6 $242.87   6.583%   $258.8581   $258.86   $258.85   $258.90  
  Purchase #7 $69.34   4.861%   $72.7106   $72.71   $72.70   $72.70  
  7 purchase totals = $839.36       $920.1484   $920.14   $920.10   $920.30