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 $125.66   6.686%   $134.0616   $134.06   $134.05   $134.10  
  Purchase #2 $208.43   8.820%   $226.8135   $226.81   $226.80   $226.80  
  Purchase #3 $176.31   13.773%   $200.5932   $200.59   $200.60   $200.60  
  Purchase #4 $169.52   12.431%   $190.593   $190.59   $190.60   $190.60  
  Purchase #5 $88.89   4.277%   $92.6918   $92.69   $92.70   $92.70  
  Purchase #6 $59.73   3.717%   $61.9502   $61.95   $61.95   $62.00  
  Purchase #7 $47.63   11.829%   $53.2642   $53.26   $53.25   $53.30  
  7 purchase totals = $876.17       $959.9675   $959.95   $959.95   $960.10