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 $132.38   5.376%   $139.4967   $139.50   $139.50   $139.50  
  Purchase #2 $215.25   7.806%   $232.0524   $232.05   $232.05   $232.10  
  Purchase #3 $99.45   6.535%   $105.9491   $105.95   $105.95   $105.90  
  Purchase #4 $179.50   9.814%   $197.1161   $197.12   $197.10   $197.10  
  Purchase #5 $161.25   9.411%   $176.4252   $176.43   $176.45   $176.40  
  Purchase #6 $66.34   4.587%   $69.383   $69.38   $69.40   $69.40  
  Purchase #7 $41.82   7.616%   $45.005   $45.01   $45.00   $45.00  
  7 purchase totals = $895.99       $965.4275   $965.44   $965.45   $965.40