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 $41.52   4.246%   $43.2829   $43.28   $43.30   $43.30  
  Purchase #2 $115.58   5.859%   $122.3518   $122.35   $122.35   $122.40  
  Purchase #3 $48.77   6.178%   $51.783   $51.78   $51.80   $51.80  
  Purchase #4 $198.79   11.795%   $222.2373   $222.24   $222.25   $222.20  
  Purchase #5 $90.70   5.720%   $95.888   $95.89   $95.90   $95.90  
  Purchase #6 $208.33   8.790%   $226.6422   $226.64   $226.65   $226.60  
  Purchase #7 $32.69   8.156%   $35.3562   $35.36   $35.35   $35.40  
  7 purchase totals = $736.38       $797.5414   $797.54   $797.60   $797.60