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 $59.92   5.524%   $63.23   $63.23   $63.25   $63.20  
  Purchase #2 $72.54   7.419%   $77.9217   $77.92   $77.90   $77.90  
  Purchase #3 $48.37   8.636%   $52.5472   $52.55   $52.55   $52.50  
  Purchase #4 $74.94   8.705%   $81.4635   $81.46   $81.45   $81.50  
  Purchase #5 $215.64   4.808%   $226.008   $226.01   $226.00   $226.00  
  Purchase #6 $166.85   4.364%   $174.1313   $174.13   $174.15   $174.10  
  Purchase #7 $209.47   10.335%   $231.1187   $231.12   $231.10   $231.10  
  7 purchase totals = $847.73       $906.4204   $906.42   $906.40   $906.30