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 $59.46   9.597%   $65.1664   $65.17   $65.15   $65.20  
  Purchase #2 $161.34   13.248%   $182.7143   $182.71   $182.70   $182.70  
  Purchase #3 $158.63   13.353%   $179.8119   $179.81   $179.80   $179.80  
  Purchase #4 $70.37   10.721%   $77.9144   $77.91   $77.90   $77.90  
  Purchase #5 $217.94   13.335%   $247.0023   $247.00   $247.00   $247.00  
  Purchase #6 $209.69   5.800%   $221.852   $221.85   $221.85   $221.90  
  Purchase #7 $229.90   12.694%   $259.0835   $259.08   $259.10   $259.10  
  7 purchase totals = $1,107.33       $1,233.5448   $1,233.53   $1,233.50   $1,233.60