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 $229.82   13.347%   $260.4941   $260.49   $260.50   $260.50  
  Purchase #2 $44.55   3.807%   $46.246   $46.25   $46.25   $46.20  
  Purchase #3 $149.79   5.458%   $157.9655   $157.97   $157.95   $158.00  
  Purchase #4 $42.36   9.215%   $46.2635   $46.26   $46.25   $46.30  
  Purchase #5 $10.88   5.844%   $11.5158   $11.52   $11.50   $11.50  
  Purchase #6 $183.86   13.320%   $208.3502   $208.35   $208.35   $208.40  
  Purchase #7 $53.89   3.576%   $55.8171   $55.82   $55.80   $55.80  
  7 purchase totals = $715.15       $786.6522   $786.66   $786.60   $786.70