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 $117.42   8.235%   $127.0895   $127.09   $127.10   $127.10  
  Purchase #2 $30.96   9.809%   $33.9969   $34.00   $34.00   $34.00  
  Purchase #3 $157.41   10.324%   $173.661   $173.66   $173.65   $173.70  
  Purchase #4 $53.53   13.207%   $60.5997   $60.60   $60.60   $60.60  
  Purchase #5 $233.96   7.700%   $251.9749   $251.97   $251.95   $252.00  
  Purchase #6 $248.45   5.140%   $261.2203   $261.22   $261.20   $261.20  
  Purchase #7 $194.62   10.399%   $214.8585   $214.86   $214.85   $214.90  
  7 purchase totals = $1,036.35       $1,123.4008   $1,123.40   $1,123.35   $1,123.50