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 $30.95   12.390%   $34.7847   $34.78   $34.80   $34.80  
  Purchase #2 $202.44   4.699%   $211.9527   $211.95   $211.95   $212.00  
  Purchase #3 $36.95   13.660%   $41.9974   $42.00   $42.00   $42.00  
  Purchase #4 $158.84   3.574%   $164.5169   $164.52   $164.50   $164.50  
  Purchase #5 $86.49   12.841%   $97.5962   $97.60   $97.60   $97.60  
  Purchase #6 $191.36   3.710%   $198.4595   $198.46   $198.45   $198.50  
  Purchase #7 $58.86   12.546%   $66.2446   $66.24   $66.25   $66.20  
  7 purchase totals = $765.89       $815.5520   $815.55   $815.55   $815.60