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 $173.34   12.419%   $194.8671   $194.87   $194.85   $194.90  
  Purchase #2 $10.73   12.153%   $12.034   $12.03   $12.05   $12.00  
  Purchase #3 $98.76   13.331%   $111.9257   $111.93   $111.95   $111.90  
  Purchase #4 $226.55   6.595%   $241.491   $241.49   $241.50   $241.50  
  Purchase #5 $212.64   4.723%   $222.683   $222.68   $222.70   $222.70  
  Purchase #6 $122.40   3.685%   $126.9104   $126.91   $126.90   $126.90  
  Purchase #7 $112.94   5.572%   $119.233   $119.23   $119.25   $119.20  
  7 purchase totals = $957.36       $1,029.1442   $1,029.14   $1,029.20   $1,029.10