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 $191.39   4.508%   $200.0179   $200.02   $200.00   $200.00  
  Purchase #2 $48.97   9.775%   $53.7568   $53.76   $53.75   $53.80  
  Purchase #3 $102.59   11.276%   $114.158   $114.16   $114.15   $114.20  
  Purchase #4 $160.35   6.785%   $171.2297   $171.23   $171.25   $171.20  
  Purchase #5 $151.88   6.275%   $161.4105   $161.41   $161.40   $161.40  
  Purchase #6 $116.85   4.511%   $122.1211   $122.12   $122.10   $122.10  
  Purchase #7 $154.76   4.435%   $161.6236   $161.62   $161.60   $161.60  
  7 purchase totals = $926.79       $984.3176   $984.32   $984.25   $984.30