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 $217.46   11.530%   $242.5331   $242.53   $242.55   $242.50  
  Purchase #2 $84.32   10.289%   $92.9957   $93.00   $93.00   $93.00  
  Purchase #3 $246.41   11.626%   $275.0576   $275.06   $275.05   $275.10  
  Purchase #4 $91.84   7.724%   $98.9337   $98.93   $98.95   $98.90  
  Purchase #5 $33.83   9.453%   $37.0279   $37.03   $37.05   $37.00  
  Purchase #6 $11.82   11.569%   $13.1875   $13.19   $13.20   $13.20  
  Purchase #7 $161.59   7.836%   $174.2522   $174.25   $174.25   $174.30  
  7 purchase totals = $847.27       $933.9877   $933.99   $934.05   $934.00