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 $22.39   6.609%   $23.8698   $23.87   $23.85   $23.90  
  Purchase #2 $226.59   8.412%   $245.6508   $245.65   $245.65   $245.70  
  Purchase #3 $44.99   7.291%   $48.2702   $48.27   $48.25   $48.30  
  Purchase #4 $226.49   5.843%   $239.7238   $239.72   $239.70   $239.70  
  Purchase #5 $46.59   6.607%   $49.6682   $49.67   $49.65   $49.70  
  Purchase #6 $227.96   4.848%   $239.0115   $239.01   $239.00   $239.00  
  Purchase #7 $92.36   13.482%   $104.812   $104.81   $104.80   $104.80  
  7 purchase totals = $887.37       $951.0063   $951.00   $950.90   $951.10