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 $51.94   13.843%   $59.1301   $59.13   $59.15   $59.10  
  Purchase #2 $185.40   8.553%   $201.2573   $201.26   $201.25   $201.30  
  Purchase #3 $174.99   12.123%   $196.204   $196.20   $196.20   $196.20  
  Purchase #4 $75.78   11.128%   $84.2128   $84.21   $84.20   $84.20  
  Purchase #5 $70.75   9.766%   $77.6594   $77.66   $77.65   $77.70  
  Purchase #6 $39.81   9.636%   $43.6461   $43.65   $43.65   $43.60  
  Purchase #7 $56.54   11.418%   $62.9957   $63.00   $63.00   $63.00  
  7 purchase totals = $655.21       $725.1054   $725.11   $725.10   $725.10