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 $182.89   13.159%   $206.9565   $206.96   $206.95   $207.00  
  Purchase #2 $112.61   12.727%   $126.9419   $126.94   $126.95   $126.90  
  Purchase #3 $178.74   11.345%   $199.0181   $199.02   $199.00   $199.00  
  Purchase #4 $208.71   8.466%   $226.3794   $226.38   $226.40   $226.40  
  Purchase #5 $156.92   4.837%   $164.5102   $164.51   $164.50   $164.50  
  Purchase #6 $93.52   4.375%   $97.6115   $97.61   $97.60   $97.60  
  Purchase #7 $114.41   10.526%   $126.4528   $126.45   $126.45   $126.50  
  7 purchase totals = $1,047.80       $1,147.8704   $1,147.87   $1,147.85   $1,147.90