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 $54.68   7.464%   $58.7613   $58.76   $58.75   $58.80  
  Purchase #2 $222.50   13.683%   $252.9447   $252.94   $252.95   $252.90  
  Purchase #3 $131.94   3.423%   $136.4563   $136.46   $136.45   $136.50  
  Purchase #4 $207.52   7.456%   $222.9927   $222.99   $223.00   $223.00  
  Purchase #5 $53.35   8.747%   $58.0165   $58.02   $58.00   $58.00  
  Purchase #6 $65.33   12.780%   $73.6792   $73.68   $73.70   $73.70  
  Purchase #7 $241.25   10.546%   $266.6922   $266.69   $266.70   $266.70  
  7 purchase totals = $976.57       $1,069.5429   $1,069.54   $1,069.55   $1,069.60