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 $93.81   4.209%   $97.7585   $97.76   $97.75   $97.80  
  Purchase #2 $51.41   6.504%   $54.7537   $54.75   $54.75   $54.80  
  Purchase #3 $189.82   9.342%   $207.553   $207.55   $207.55   $207.60  
  Purchase #4 $234.71   13.858%   $267.2361   $267.24   $267.25   $267.20  
  Purchase #5 $130.25   3.852%   $135.2672   $135.27   $135.25   $135.30  
  Purchase #6 $250.80   10.724%   $277.6958   $277.70   $277.70   $277.70  
  Purchase #7 $69.26   8.108%   $74.8756   $74.88   $74.90   $74.90  
  7 purchase totals = $1,020.06       $1,115.1399   $1,115.15   $1,115.15   $1,115.30