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 $55.47   10.130%   $61.0891   $61.09   $61.10   $61.10  
  Purchase #2 $225.62   3.831%   $234.2635   $234.26   $234.25   $234.30  
  Purchase #3 $148.32   7.374%   $159.2571   $159.26   $159.25   $159.30  
  Purchase #4 $63.82   12.709%   $71.9309   $71.93   $71.95   $71.90  
  Purchase #5 $93.29   5.515%   $98.4349   $98.43   $98.45   $98.40  
  Purchase #6 $141.25   10.834%   $156.553   $156.55   $156.55   $156.60  
  Purchase #7 $202.69   5.769%   $214.3832   $214.38   $214.40   $214.40  
  7 purchase totals = $930.46       $995.9117   $995.90   $995.95   $996.00