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 $240.90   11.238%   $267.9723   $267.97   $267.95   $268.00  
  Purchase #2 $48.50   10.127%   $53.4116   $53.41   $53.40   $53.40  
  Purchase #3 $191.52   12.293%   $215.0636   $215.06   $215.05   $215.10  
  Purchase #4 $225.33   11.222%   $250.6165   $250.62   $250.60   $250.60  
  Purchase #5 $231.40   4.750%   $242.3915   $242.39   $242.40   $242.40  
  Purchase #6 $250.81   11.161%   $278.8029   $278.80   $278.80   $278.80  
  Purchase #7 $148.92   3.542%   $154.1947   $154.19   $154.20   $154.20  
  7 purchase totals = $1,337.38       $1,462.4531   $1,462.44   $1,462.40   $1,462.50