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 $46.76   13.836%   $53.2297   $53.23   $53.25   $53.20  
  Purchase #2 $173.66   3.545%   $179.8162   $179.82   $179.80   $179.80  
  Purchase #3 $132.34   3.795%   $137.3623   $137.36   $137.35   $137.40  
  Purchase #4 $208.76   11.235%   $232.2142   $232.21   $232.20   $232.20  
  Purchase #5 $50.40   3.477%   $52.1524   $52.15   $52.15   $52.20  
  Purchase #6 $80.71   4.867%   $84.6382   $84.64   $84.65   $84.60  
  Purchase #7 $231.85   6.402%   $246.693   $246.69   $246.70   $246.70  
  7 purchase totals = $924.48       $986.1060   $986.10   $986.10   $986.10