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 $230.99   6.756%   $246.5957   $246.60   $246.60   $246.60  
  Purchase #2 $122.46   9.115%   $133.6222   $133.62   $133.60   $133.60  
  Purchase #3 $210.59   12.312%   $236.5178   $236.52   $236.50   $236.50  
  Purchase #4 $46.26   4.640%   $48.4065   $48.41   $48.40   $48.40  
  Purchase #5 $65.98   12.568%   $74.2724   $74.27   $74.25   $74.30  
  Purchase #6 $22.40   10.109%   $24.6644   $24.66   $24.65   $24.70  
  Purchase #7 $156.87   9.392%   $171.6032   $171.60   $171.60   $171.60  
  7 purchase totals = $855.55       $935.6822   $935.68   $935.60   $935.70