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 $60.67   12.483%   $68.2434   $68.24   $68.25   $68.20  
  Purchase #2 $180.63   9.476%   $197.7465   $197.75   $197.75   $197.70  
  Purchase #3 $71.85   8.638%   $78.0564   $78.06   $78.05   $78.10  
  Purchase #4 $105.64   10.193%   $116.4079   $116.41   $116.40   $116.40  
  Purchase #5 $165.47   10.457%   $182.7732   $182.77   $182.75   $182.80  
  Purchase #6 $65.66   11.585%   $73.2667   $73.27   $73.25   $73.30  
  Purchase #7 $198.44   10.385%   $219.048   $219.05   $219.05   $219.00  
  7 purchase totals = $848.36       $935.5421   $935.55   $935.50   $935.50