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 $136.38   7.376%   $146.4394   $146.44   $146.45   $146.40  
  Purchase #2 $177.52   8.466%   $192.5488   $192.55   $192.55   $192.50  
  Purchase #3 $39.58   8.824%   $43.0725   $43.07   $43.05   $43.10  
  Purchase #4 $208.40   4.389%   $217.5467   $217.55   $217.55   $217.50  
  Purchase #5 $123.36   6.711%   $131.6387   $131.64   $131.65   $131.60  
  Purchase #6 $165.92   10.138%   $182.741   $182.74   $182.75   $182.70  
  Purchase #7 $125.76   7.768%   $135.529   $135.53   $135.55   $135.50  
  7 purchase totals = $976.92       $1,049.5161   $1,049.52   $1,049.55   $1,049.30