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 $125.38   13.674%   $142.5245   $142.52   $142.50   $142.50  
  Purchase #2 $210.46   8.284%   $227.8945   $227.89   $227.90   $227.90  
  Purchase #3 $204.91   10.137%   $225.6817   $225.68   $225.70   $225.70  
  Purchase #4 $7.93   9.454%   $8.6797   $8.68   $8.70   $8.70  
  Purchase #5 $58.93   7.705%   $63.4706   $63.47   $63.45   $63.50  
  Purchase #6 $33.50   4.599%   $35.0407   $35.04   $35.05   $35.00  
  Purchase #7 $237.77   9.636%   $260.6815   $260.68   $260.70   $260.70  
  7 purchase totals = $878.88       $963.9732   $963.96   $964.00   $964.00