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 $48.52   13.726%   $55.1799   $55.18   $55.20   $55.20  
  Purchase #2 $148.82   6.110%   $157.9129   $157.91   $157.90   $157.90  
  Purchase #3 $166.79   3.159%   $172.0589   $172.06   $172.05   $172.10  
  Purchase #4 $125.69   13.566%   $142.7411   $142.74   $142.75   $142.70  
  Purchase #5 $48.30   11.526%   $53.8671   $53.87   $53.85   $53.90  
  Purchase #6 $222.75   6.787%   $237.868   $237.87   $237.85   $237.90  
  Purchase #7 $96.81   8.197%   $104.7455   $104.75   $104.75   $104.70  
  7 purchase totals = $857.68       $924.3734   $924.38   $924.35   $924.40