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 $46.97   8.563%   $50.992   $50.99   $51.00   $51.00  
  Purchase #2 $209.98   10.663%   $232.3702   $232.37   $232.35   $232.40  
  Purchase #3 $63.67   7.587%   $68.5006   $68.50   $68.50   $68.50  
  Purchase #4 $109.59   12.189%   $122.9479   $122.95   $122.95   $122.90  
  Purchase #5 $123.83   9.823%   $135.9938   $135.99   $136.00   $136.00  
  Purchase #6 $85.86   8.860%   $93.4672   $93.47   $93.45   $93.50  
  Purchase #7 $82.72   11.255%   $92.0301   $92.03   $92.05   $92.00  
  7 purchase totals = $722.62       $796.3018   $796.30   $796.30   $796.30