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 $162.33   8.697%   $176.4478   $176.45   $176.45   $176.40  
  Purchase #2 $108.86   8.724%   $118.3569   $118.36   $118.35   $118.40  
  Purchase #3 $41.90   5.821%   $44.339   $44.34   $44.35   $44.30  
  Purchase #4 $241.74   11.451%   $269.4216   $269.42   $269.40   $269.40  
  Purchase #5 $35.92   13.607%   $40.8076   $40.81   $40.80   $40.80  
  Purchase #6 $94.48   3.792%   $98.0627   $98.06   $98.05   $98.10  
  Purchase #7 $179.76   4.150%   $187.22   $187.22   $187.20   $187.20  
  7 purchase totals = $864.99       $934.6556   $934.66   $934.60   $934.60