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 $84.71   13.396%   $96.0578   $96.06   $96.05   $96.10  
  Purchase #2 $66.50   4.621%   $69.573   $69.57   $69.55   $69.60  
  Purchase #3 $69.71   8.743%   $75.8047   $75.80   $75.80   $75.80  
  Purchase #4 $139.52   5.874%   $147.7154   $147.72   $147.70   $147.70  
  Purchase #5 $42.40   8.869%   $46.1605   $46.16   $46.15   $46.20  
  Purchase #6 $129.47   5.515%   $136.6103   $136.61   $136.60   $136.60  
  Purchase #7 $39.32   5.112%   $41.33   $41.33   $41.35   $41.30  
  7 purchase totals = $571.63       $613.2517   $613.25   $613.20   $613.30