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 $59.39   13.118%   $67.1808   $67.18   $67.20   $67.20  
  Purchase #2 $146.90   9.775%   $161.2595   $161.26   $161.25   $161.30  
  Purchase #3 $125.75   11.438%   $140.1333   $140.13   $140.15   $140.10  
  Purchase #4 $208.95   5.235%   $219.8885   $219.89   $219.90   $219.90  
  Purchase #5 $219.64   6.827%   $234.6348   $234.63   $234.65   $234.60  
  Purchase #6 $101.69   9.872%   $111.7288   $111.73   $111.75   $111.70  
  Purchase #7 $59.40   9.592%   $65.0976   $65.10   $65.10   $65.10  
  7 purchase totals = $921.72       $999.9233   $999.92   $1,000.00   $999.90