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 $129.41   13.560%   $146.958   $146.96   $146.95   $147.00  
  Purchase #2 $235.76   11.438%   $262.7262   $262.73   $262.75   $262.70  
  Purchase #3 $231.38   10.157%   $254.8813   $254.88   $254.90   $254.90  
  Purchase #4 $227.53   11.539%   $253.7847   $253.78   $253.80   $253.80  
  Purchase #5 $115.40   7.449%   $123.9961   $124.00   $124.00   $124.00  
  Purchase #6 $81.96   5.193%   $86.2162   $86.22   $86.20   $86.20  
  Purchase #7 $123.97   10.210%   $136.6273   $136.63   $136.65   $136.60  
  7 purchase totals = $1,145.41       $1,265.1898   $1,265.20   $1,265.25   $1,265.20