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 $115.53   5.857%   $122.2966   $122.30   $122.30   $122.30  
  Purchase #2 $175.99   10.731%   $194.8755   $194.88   $194.90   $194.90  
  Purchase #3 $191.72   8.831%   $208.6508   $208.65   $208.65   $208.70  
  Purchase #4 $43.71   11.849%   $48.8892   $48.89   $48.90   $48.90  
  Purchase #5 $208.38   12.149%   $233.6961   $233.70   $233.70   $233.70  
  Purchase #6 $75.33   4.244%   $78.527   $78.53   $78.55   $78.50  
  Purchase #7 $23.32   5.702%   $24.6497   $24.65   $24.65   $24.60  
  7 purchase totals = $833.98       $911.5849   $911.60   $911.65   $911.60