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 $208.41   13.626%   $236.8079   $236.81   $236.80   $236.80  
  Purchase #2 $207.38   10.243%   $228.6219   $228.62   $228.60   $228.60  
  Purchase #3 $112.35   11.256%   $124.9961   $125.00   $125.00   $125.00  
  Purchase #4 $178.97   3.136%   $184.5825   $184.58   $184.60   $184.60  
  Purchase #5 $173.33   6.864%   $185.2274   $185.23   $185.25   $185.20  
  Purchase #6 $241.61   10.334%   $266.578   $266.58   $266.60   $266.60  
  Purchase #7 $45.93   10.382%   $50.6985   $50.70   $50.70   $50.70  
  7 purchase totals = $1,167.98       $1,277.5123   $1,277.52   $1,277.55   $1,277.50